Patch 5 broke the game's ability to load any modded save that has had any mods removed. It is... unfortunate. There is a workaround posted on Nexus mods for now. It seems to work for some people: https://www.nexusmods.com/baldursgate3/mods/4767?tab=description
Thanks! I will look into this workaround as soon as I can muster up the motivation again for investing more time in fixing bugs than actual gameplay.