Interesting start, and kudos on allowing players to skip!
One minor nitpick I got was that the Thick Fog title would feel better had it more of a smooth movement instead of just switching between straight and bent state, if that makes sense.
The settings menu feels a bit off because I can't see the minimum and maximum points, actually, now that the cloud passed I can see it, maybe make it a different shade or add some outline?
The dialogue didn't convey much emotion, sometimes it felt like someone just reading lines instead of a tired man talking about cleaning the mirror. Also I had to decrease the music a lot to hear it when the spirit appeared.
It seems to be adding clicks to a queue, I clicked the door multiple times and it kept on activating its dialogue reaction even after I left to some other room.
I played the bird song to the spirit but I guess I had something wrong in the combination, so nothing changed. That made me quit because it was too long to play all the horn parts.
Overall I liked the setting and the art style kind of grew on me, but the puzzle was too harsh/boring. Maybe if we could play the horn before the sound ended?