Thank you! I already got some feedback that going back to the start after killing a boss wasn't great from a gameplay perspective, and I can definitely see it being less clear than I intended as well. Most likely I would opt to use a short cutscene for that purpose instead if I made some changes. Audio was just something I didn't have time for.
The resolution is pretty low. I did my testing in just the small Unity preview window, and didn't realize until I was making builds a few hours before the submission deadline that I didn't make my UI scale to window size and had to just build with a low resolution to make it work.