So I had the same problem on the PS5.
The only way I've seen to fix it is to go back to a save point before you took the quest. Do all the other quests before you accept Last Rites. When I did that, I was able to easily complete the quest.
I think the issue is that there is another quest marker smack in the middle of this one and for some reason Last Rites will bug out if accepted while that quest is still in play. (The Hidden Hoard quest).
I'm on PS5 and already completed hidden hoard and the issue is still there so, I think the quest itself is just broken.
