Not sure why these crashes would only happen during BG3 sessions though if it is the PSU - I’d surely be getting them elsewhere too especially whilst stress testing or playing other intensive games?
I don't agree with the other commenter about it being the PSU; an 850W PSU should handle those specs easily. There are dozens of things it could be,though, and going through each and every one will take tons of time. That said, one could e.g. start with downclocking the CPU, GPU and GPU's VRAM and system RAM, move the game to the other SSD and then seeing if it still continues to do it or not. If the issue disappears, then proceed to turn only one of those things back the way it was at a time and seeing when it begins to crash again.
