It seems like my copy of the game is bricked.
In my first playthrough I chose to lose immortality, then the skull, heart, and bone debuffs. I was stuck at the end of the fourth level and I couldn't choose any of the remaining powers to lose. None of the powers were selectable, so I could not proceed.
Is this bugged? Not sure why I couldn't click any of the three options that should have been available to me. The pause menu is also broken insofar as I cannot click any option, and when I force-quit the game and restarted I found I can't select any power to lose after finishing the tutorial stage.
I posted this in a comment on the Steam discussions page, but it seems like there's no support for the game.