You are looking for niche channels that focus on one subject from a subject matter expert like Historia Civilis (Roman history), The Great War Channel (WW1) and Military History Visualized (WW2). Channels like these draw from current respected primary sources and secondary sources i.e. Caesar's own Memoirs, Bundeswehr Military Archives, When Titans Clashed by David Glantz ect. They cover narrow topics that they are well-versed in.

Even then be cautious, you can run into problematic channels like TIK and lindybeige that refer to respected sources (TIK references the same book When Titans Clashed by David Glantz for example) but draw wildly wrong conclusions. In this video TIK claims the Nazis abolished private property.

Spoiler: they didn't

The broader the channel's subject, the harder to keep the documentaries engaging accurate and concise. That is not to say pop history channels like Crashcourse History's and Extra Credit's are always bad. They can be good, but they sacrifice lots of accuracy to fit in 10 minutes. They have to research every video on a different subject and it shows. One particularly bad example is Extra Credit's Ottoman Empire series which relies on outdated and frankly racist scholarship in Suleiman the Magnificent by André Clot. This kind of issue is common in pop history channels that cover many time periods.

A documentary on Soviet Farming Practices between 1972 and 1974 is going to be much more accurate than a documentary on the Soviet Union.

I hope this helps.

Edit: formatting mobile