The story is confusing, the few intro text sentences just say that you are going on a run and then when it disappears you are suddenly in some abandoned mansion with no context as to how you got there and what you are supposed to be doing (and why). It would've been better to leave out the intro text entirely rather than to have such a jarring transition. But ideally, you should give this game a proper intro.
The monster blinds the main character for as long as he looks it in the... headlight, I guess. I don't think it's implemented very well. It would be better if the effect was more progressive, maybe it starts off as a lightly obscuring effect that grows in intensity the longer you are looking towards the monster. And instead of disappearing immediately as soon as you look away, the main character's eyes would take some time to adjust to the darkness again, with the blinding effect being reduced in intensity with each second.
Opening the doors is a chore due to the weird control scheme where you for some reason have separate buttons for opening and closing them. Whatever the reason for that, it just makes the game frustrating to play. So, if you just got rid of that and had a single Interact key, that would already drastically improve the gameplay.
The rooms you are opening to turn off the lights seem to be a great way to get a game over, since the monster can block the entrance and trap you there with no hope of getting out. Maybe they could become a safe area once you turn off the light switch/destroy the mirror inside?
The monster reactivating the lights you turned off as it walks by them seems interesting, but ultimately it's way too much, since you have to turn off all 21 of them. It could work if maybe there were less of them, but this way it just makes your efforts feel pointless. Some way to fight back against the monster would also be welcome, maybe the mirrors were supposed to provide a way for that, but they don't seem to do anything at this point.
The monster also seems to be way too relentless and there's not really a clear idea as to what you are supposed to do to survive against it. Running doesn't seem very effective and you can run into it easily since whatever signs that it is nearby are so subtle that you can miss them easily.
The main character's flashlight isn't very good. I don't think it's made correctly? I think a decent flashlight effect needs to be made from two separate parts in order to get a realistic flashlight and this one just seems flat and doesn't really let you see that much. I guess you should look up some tutorials on how to make a flashlight effect in the engine you used (Unity, I think) in order to improve it.
Other then the MC's flashlight, the overall presentation is decent. The main menu seems to be a placeholder though.
Anyway, good job! You have an interesting prototype of a game there. It just needs a lot of work, but it does have potential to be a good game!