This demo is pretty cool ! It's a bit too short to my liking (only one boss is not much) but the artstyle is very cool and the gameplay, although lacking of some variety, is promising. The game could benefit from quicker attacks (for enemies) to make them an actual menace and an obvious upgrade is adding other weapons (well, spells but shh) such as a "shotgun" which spreads low-damage bullet in a radius in front of the character or a slow-to-fire spell with heavy damages. One more thing, I believe you can export a Linux version on Unity and I would love if you ever do so (even if it's in 10 versions), it's easy to do on your side and it avoids compatibility problem on player's.
Ps: I think you forgor to remove the folder called "Witch's Dungeon_BurstDebugInformation_DoNotShip" which (as the name says) shouldn't be shipped