Scandinavia is a region for which I hold a particular interest, but I hardly see it talked about. The suggested reading list for the subreddit lists almost no resources regarding this region and I find it just as difficult to find scholarly research and studies about it online.
For someone seeking more in-depth insight into this subject, where should I look?
Can you specify time periods and/or countries?
Not OP, but how about the periods from the 13th to 16th centuries?
I believe /u/joshiguy1 means Arkiv Digital as the Swedish counterpart. It does require a subscription, and I wouldn't recommend getting one unless you feel comfortable reading old handwriting (transscriptions aren't included). Another similar site that might be of interest is Digital Museum, which shows objects, and information about those, from Scandinavia mostly.
As to why the book list is lacking on that part... Well, for one, there aren't a whole lot of questions about Scandinavia on here, so naturally there isn't the same "pressing need" for it either. There is also the issue with most books about Scandinavia being written in the native languages, and since this is a mostly English-speaking forum, those seem redundant to include.