Manaflower: Fortunately Anchor is optional, so I was able to beat the game ignoring it, but it's still a huge bummer.
Still, I experimented with it a little more and checking some videos about the fight in hopes of finding a solution, and the crash seems to coincide with the boss's attack.
My ability to debug this has reached its limit besides just changing my GPU driver (currently 452.06). If I have the energy, I guess I could try studio drivers since they're supposedly more stable, but there's nothing really pointing at it being driver issue (though I suppose it could be deeper seated issue).
argenisX: This must be an RTX specific bug, there's a lot more people having the issue.
The fixes for this are (and believe me this is a bit crazy)
1)Turning the audio to 0 on the settings of the game before entering the fight
2) Settings the resolution to less than the full screen resolution of your monitor
3) Playing the game in compatibility mode, specifically Windows Vista mode
Give those all together a try, that's a bit insane, considering that the boss itself is also kinda hard to beat until way later on.
It's not RTX specific. I have a non-RTX Nvidia-GPU (with the latest driver) and the same issue.