This game has a fun concept and I coomend you for going thru with completing your project as a solo (?) dev. I like the way the light theme is clearly displayed as a central mechanic and the graphics utilize it appropriately. The backtrack changing with the state of the character was also an interesting touch to showcase the state of mind the player character is in. That said, there are some concerns I had with mechanics.
For a game like this where the main gameplay emphasizes quick and precise movements (especially given the fast and unreplenishable sanity meter), the movement just doesn't suffice. There is a major bug that occurs when the player tries to change direction while the character is moving, causing them to continue moving in the same direction they were walking in before. This forces the player to have to slow down and wait until the character stops moving to switch to another direction, which increases the time they're in the dark, making it even harder than need be to find what they need. Additionally, I think that while the idea of collecting keys to unlock doors is a classic and familiar concept that people are used to, it could have been done better by indicating which keys go to where. If there were less doors, floors and keys overall, this wouldn't be as much of an issue since it would be more obvious, but because there are so many doors to unlock, not having any kind of indication makes it so it is virtually impossible to win with the quick sanity drain, difficult movement, and overabundance of darkness unless you are the developer yourself.
That said, this isn't the worst game I've seen and I think there's some potential to the idea, but it definitely needs some polish and a little reworking of values to make it achievably fun. All in all, I hope you have a good day :)