When completing a section of the Monolith of Fate, if your controller (in my case PS5 via cable) is plugged in when defeating the boss the game will promptly close to desktop. This is consistently reproducible, and by unplugging my controller to fight the boss on M/KB, I can avoid the crash 100% of the time.
https://www . reddit . com/r/LastEpoch/comments/1k39xhu/crashing_on_quest_completion/
Game crashes after completing a Monolith - #10 by Psojed