I have the same issue with BG3 and with Starfield on my new installed GeForce rtx 3060 but when I replace it with my old GeForce gtx 1650, the game runs (bad of course because of crap video card) without PC shutting down. I believe this is because my old cpu Intel 3770 doesn't generate enough juice to feed my rtx 3060. My 700w psu is more than enough for my system