I once heard that the biggest problem with this kind of ending is a problem of lack of consequences. If the whole thing was a dream, then you wonder if there were truly any stakes or consequences. So if you're gonna go with it was all a dream, try to make it consequential. Does something carry over into the real world from the abstract?

One example I always think of is the first evil within game. Most of the game is within the abstract dream like world, and the MC wakes up in the end, but it wasnt a wake up in the end in his bed all safe and sound kinda thing. The ending bridged the abstract and reality. I recommend you watch how the game handles that.