It's definitely a BG3 issue and I am confident that Larian will eventually fix it. It seems that we are all experiencing the same crash, and it's a critical one - very unlikely that all of our PSUs are suddently faulty. If you haven't done already, please submit a bug report.
Personally, I followed Kbottt's advice above and my issue has improved/resolved.
MY TEMPORARY FIX:
At the beginning I was getting this crash after 30 minutes to 1.5 hours of gameplay. It was happening during dialogue, combat or even character creation. It happened thrice before I started tinkering with solutions, including updating drivers, lowering gpu voltage (alt+z), reinstalling game and changing my PSU entirely. In total I think it happened around 12 times before I stopped trying. In order to protect my PC.
A few days ago I tried Kbott's solution - went to bios and put a power limit to my CPU (also I disabled all stock "overclock" configurations since I have a gaming z170 mobo). After doing that I was able to have an 8 hour session, before I had another crash. Originally, I was rarely passing the one hour mark so I was/am hopeful that this can be a temporary fix. I then went back to the bios and undervolted the cpu even more (basically I chose the highest power limit possible) and since then I had 3, long, uninterrupted sessions. I will edit this post if I encounter a crash again, but for now the game is playable.
More detail:
Similar to Kbott above, my cpu temps were and are fine on the overlay - so if a spike is happening it is very fast. I have a 12700k and the Be Quiet Dark Rock Pro 4 which is considered one of most effective cpu coolers, so if the issue is actually temp-related I don't think that upgrading/changing your hardware will help. Furthermore, even with the most extreme undervolting option I saw no/negligible performance loss, I am steadily at 60 (frame limit) frames in 4k. However, I also loaded my ultra-modded skyrim installation and the fps reduction was ridiculous, so if this fix works for you too, you should expect that you will have to go back to the bios and change the values for other demanding games or work. Finally, I also removed the power limit of my GPU a few days in and the crash did not reappear, so I suppose it is unrelated to the gpu.
