Did you have a windows 10 update?
I'm having a similar experience. My computer was having no issue running the game on Ultra until a windows update last week, now Baldur's Gate 3 struggles to load assets, I've had a few crashes, and prolonged time with t-poses. This happens on all graphic settings now. (I've gone through all the FAQ suggestions from Larian).
Also my computer only has 8GB of ram. I've been waiting for patch 4 to find out if I should upgrade my ram.
