Aight, made an account just to thank you guys. You people fixed the issue for me ! Super cool team effort guys from all of you in the discussion; thanks me for letting me play the game.
Anyways, i confirm that ITS NOT JUST THE HELLFIRE WATCHERS!
Personally for me it was a 7 HP Body in the Blushing Mermaid basement. and it was hidden was in the BLOODY WATER. Thanks god I found it and reduced it to 0 HP with an AoE spell. Not sure if the cursed mask interaction that those guys wear is what was causing it.
Will keep you posted if the crash comes back at some point but it seems that I can travel freely back and forth from Lower City now, which I absolutely couldn't before.
As for Larian well... BG3 is for sure one of the best games I have ever played but .. and it hurts me to say that seriously given how much I love the game... an unadressed bug this big (literally making it 100% impossible to finish the game) is a serious issue for a product sold to over 5 mln customers.