Hi! I'm a PhD candidate and have dealt with accessibility issues during the Covid pandemic, which affected my dissertation work. I study late medieval Germany, so luckily I was able to regain access to German archives this year. Here are a few suggestions that might help you:

1. Consider the scope of your project and timeline. I understand that you are thinking longterm, but you might want to start with the more accessible research locations for your current project(s) to build your research skills. If you are in a program and need to complete a thesis/dissertation, then look for a project that is achievable in the space of that program. For me, it looked like reducing my case studies, adjusting my research questions, and looking for digital sources. I was sad to pause some parts of my project, but I know I'll get back to those case studies in the next phase of my career. Right now, I just need to finish my degree.
2. Look for digitized sources and materials. During covid many repositories began digitizing a lot of their materials. While it's not the same as in-person engagement with archival objects, digitized sources do still offer a lot for historians and there's a lot more available now. You could also see if an archivist would work with you remotely and digitize materials for you (you'll just need to budget for that).
3. Reach out to scholars who work in your subfield. They may have access to materials they can share with you and/or connect you to people in their network, including archivists and librarians. They can also give you invaluable tips about working abroad, specific to the regions and institutions you want to work in.
4. Look for materials/sources housed outside of inaccessible locations. If you are doing oral histories, you could connect with dislocated/remote populations in the diaspora. If you are doing history from earlier epochs, you could look for collections in other countries with materials from Ukraine/Russia/Belarus.
   I found that in person engagement with the cultures, locations, and archival materials has been really important to me, especially in my growth as an historian. If you have the option to work on an area where you can directly engage with that culture, I highly recommend, but know that it's not impossible to study a location where you can't travel.

As I'm quite young, there's a concern I'll be taken less seriously compared to those who travel.

It's not so much that you will be taken less seriously than those who travel; it's that you may not have access to the archives you need for your research in the first place if you can't travel.

If you are interested in researching, say, the effect of Peter I's reforms on orthodox monasteries, you may need to look at the archives of dozens of monasteries from, say, 1725-1750. These may have been moved to a central location, but have likely not been digitized, so the only way to look at them would be to travel.

As always, caveat that I'm primarily a historical archaeologist - not a capital "H" historian, but I went through a similar experience for my MA. Fieldwork is typically considered a critical part of anthropological/archaeological research - this is changing in some ways - but most people still spend at least a year in the field for their dissertation, for example. My original research plan was to travel to Bolivia and excavate a roadside site associated (hopefully) with republican and/or colonial period traffic. My research was initially delayed by political instability following the 2019 election, and then when COVID hit on top of that it became clear that I wouldn't be able to travel in order to do fieldwork in the time it normally takes to finish a masters degree. So, I changed my project in a couple of ways to address that.

Firstly - the "history" part of historical archaeology became much more important. Whereas before documents would've helped shed light on material culture, documents became the central part of my thesis. I worked with collections in the united states, and material available digitally - everything from 18th century literature to colonial government documents to maps.

Secondly - I wrote a chapter experimenting with geospatial methods and publicly available satellite elevation data to create a GIS model of the road I was interested in. It's a bit much to explain here, but I tried to argue that creative use of GIS software and remote sensing data could help support certain interpretations of the historical documents, primarily by modeling the ways that different groups of people moved along the road. All of this I was able to do from my office using data from NASA and some geo-referenced historic maps.

Finally - I expanded the scope of my archaeology chapter both spatially and chronologically. Rather than looking for colonial sites that had been excavated in the specific region I was interested in - there aren't many - I looked for many examples across the continent that I could analyze in a comparative way. I also looked at archaeological publications on Andean roads, infrastructure, and lodging going back several hundred years. This helped me place later developments in context, and it also helped pad out the length of my archaeology chapter given that I couldn't collect my own data. All of these publications were available without traveling, either through ILL or digitally. It will depend on your specific research questions as to whether sufficient sources are available this way.

Basically, I did what I could with what I had, and my advisor was understanding about the factors outside of my control.

Luckily I decided not to apply for my PhD on Narodism in 19th century Russia this year, but I did attend a seminar specific to research issues with Russia, which I can relate. Firstly, it's of course heavily dependent on your subject area, but you may still be able to conduct firsthand research in neighbouring countries, with info about Russia. As just one example, Tblisi was the regional administrative capital of the entire Caucasus under the Russian Empire, so the Georgian National Archives hold a lot of Russian documents from that era. It's worth checking the archives of neighbouring states to see whether they have anything potentially useful, especially ones where the Soviets left in a hurry in the 90's and didn't take their papers with them. This does create language issues though; Russian is, of course, a global language and there are many many Russian speakers in countries other than Russian or Belarus. However, another fallout of the war aside from access issues is that Russian may as a consequence of the war have less currency as a lingua franca in places like Finland, Georgia or Estonia, which makes communicating with archivists a lot more difficult.

Beyond that, it's worth searching for digitised material. 'rusarkhiv' was one recommendation, but I can't link it since i can't access .ru sites. I don't want to give the wrong impression- it can still be done, but the outlook appears very very bleak. It's been enough to ward me off any further study in the region.

I know this was a very pragmatic answer- there is of course a far more philosophical question of whether firsthand archive work is a prerequisite to writing about a topic, that I don't feel equipped to answer and I'm sure somebody else in the comments will do more capably. But I hope this helped

This was actually a major issue for Russia before, when it was part of the Soviet Union. For much of it's existence the USSR did not allow foreign scholars into archives (or into the country as a whole), and those who were granted access were heavily restricted in what they could review.

To work around this, they used what they could. The Soviet government did publish official documents for a variety of things, especially economic output, and while those numbers were always taken with careful consideration, they were largely the best available. Other materials would also be released, in part, to the West, so scholars used what they could: official publications (the Soviets of course had their own scholars writing on things), people attending international conferences (even during Stalin Soviet academics did travel abroad), and so on. Emigres and the like also became a valuable source of information, as they published memoirs and discussed what they knew. And starting in the 1960s and continuing until 1991 Western scholars were allowed to visit and even research in the archives, though as noted access was limited and case-dependent.

The downside to all this is that there was some things that simply couldn't be properly studied. In your example actually, religious documents would have likely been restricted to some degree at this time, unless you were able to convince Soviet archivists and officials that you were writing on it from a socialist slant. Otherwise material like that was not likely to be released. As noted, nearly anything about the economy had to be largely taken at face value, even though it was known to be slanted. Sociology and related research (like most political science) was also nearly impossible, as a foreign scholar was not going to get approved to approach random Soviet citizens (nor would they have been likely to answer any questions); for this the bulk of early information was based on a research project Harvard conducted in the years after the Second World War (the Harvard Soviet Interview Project), in which hundreds of Soviet emigres and refugees were interviewed in-depth about life in the Soviet Union.

There is a good book on the struggle of contemporary Soviet scholars from the US worth reading: Know Your Enemy: The Rise and Fall of America's Soviet Experts by David C. Engerman (2009). It isn't focused on historians per se, but more contemporary studies (economics, politics, sociology, etc), and how the researchers did that, from 1945 to 1991. There's also a chapter on the Harvard Interview Project which is really worth reading in and of it's own.

I'd also suggest reading Red Flag Unfurled: History, Historians, and the Russian Revolution by Ronald Grigor Suny (2017). While it's focused on the October Revolution of 1917 and how it was interpreted in the past century, Suny looks at the difficulties of properly writing about it when the Soviet side was all but closed to most scholars (in his opinion it led to an overreliance on memoirs from those who fled, who were overwhelmingly anti-Bolshevik, so it was quite one-sided).

I'll also note a memoir of a historian who managed to do research in Moscow in the 1960s: A Spy in the Archives: A Memoir of Cold War Russia by Sheila Fitzpatrick (2015). Fitzpatrick is a leading historian on the social history of the Soviet Union, and this look at her work for her PhD dissertation shows the lengths a Westerner (in her case, an Australian studying in the UK) had to do to get access to the Soviet archives. She was one of the first to do so, and it's quite informative, as well as an engaging look at contemporary life in 1960s Moscow.