Sounds like you're going to find some excellent resources in the US too. I'm wondering when you're planning to visit? Loved your comment on your bio page, 'Scandinavian societies give me hope for the future of all people.' AWWW totally agree.
Is Skansen autumn craft festival the ultimate opportunity for such things? While it looks interesting, and frankly I love Skansen, https://skansen.se/en/see-and-do/non-bookable-activities/autumn-market/, I don't see anything about classes. Hmmm you do bring up what looks like a very fun event so thanks! Will try to make it into Stockholm one of those days. The times I've been to Skansen there were brief demos on things like making flat bread, and perhaps you can observe people working on looms, but I just don't see anything that meets what you're asking for - a few days of classes. Maybe email Skansen to ask about classes?
The other place that's incredibly rich in early Swedish history is the History Museum (Historiska Museet) in Stockholm, it's a gem, incredibly well curated and you can start downstairs in the oldest part of the exhibit and literally walk through artifacts from each century, well worth a few hours! https://historiska.se/.
Which by the way, it looks like they have some short classes in ancient crafts during the summer, but I'm guessing it's just a brief intro. Why don't you email the museum and ask them? What a great place, sigh, was just there in May and will have to go back for 'Viking Summer'. You can bake Viking-era bread and try handicrafts, clothes and Viking-era games.https://historiska.se/kalendarium/2024/06/29/vikingasommar-kul-utomhus-2/
I've heard people being disappointed in Birka. Several Swedes recommended I go there, but then it turned out they'd heard about it all their lives but not actually been! Personally, I found Birka disappointing, despite going with a wonderful guide for a 1/2 day scenic trip via boat to the island. Yes, it's historically important & there's a small museum and some outlines of a settlement, but as a non-historian, there's just not that much to actually SEE. So if you're interested in a picturesque place to visit with some (later) Viking history, I would go to Gamla (Old) Uppsala, about a 20-minute bus ride from the Uppsala train station, with several Viking royal graves and an excellent small museum, after first visiting the Swedish History museum. Hope some of that's helpful and good luck!