Hey, I don't think the game should softlock after obtaining Ending 4 in fullscreen.
EDIT: I was also going for the final ending: after I interacted with the rabbit toy for the second time, I played up until the scene in which Roza sleeps on the sofa. The game softlocked there, too. This happens in both windowed mode and fullscreen.
Edit 2: I got past the sofa scene by deleting the offending video.