Issue with Steam Deck: realm of darkness bosses just stand there

I went to do the Realm of Darkness to get energy stones or whatever and the boss just stood there. I couldn't damage it by hitting it because the pink gem wasn't exposed. So, I ran into it a bunch to die. It brought me back to the arena but then the boss was totally missing. I had to exit the game entirely.

Is anyone else having this issue on Steam Deck? Is there any way to fix this?