For me it’s dark souls after the lordvessel. The areas in that section are the worst part of the game IMO.
Also in dmc5 I hate having to play V’s missions, luckily you can skip them with the mission select, but you still have to play through them at least once when unlocking a new difficulty.
I also recently replayed cyberpunk 2077 and while I did generally enjoy the game, the ending was a slog and I had to force myself to finish it.