Somehow you managed to make the level completion effect a jumpscare in its own right and I'm not sure how to feel about that.
But more seriously, this game definitely has a neat idea, and it is pretty well executed. While some more ambient sound could be nice, the lack of it definitely does build tension. And seeing the screen start shaking when you have no clear idea where the ghost is is quite nerve-wracking.
The addition of keys to track down in later levels is interesting, but I do wish you had a little more time to see where they were located before the level goes dark. (I didn't end up playing past the first key level, so I dunno if anything more gets added afterwards.)
One thing I feel like it could use is a sense of progression. Without clear visual distinctions or a level counter, it took me a bit to make sure that there were actually distinct levels and I wasn't just mis-remembering layouts.
And lastly, one mechanic that could have been cool to add would be the ability to do a hard knock on a wall, which would reveal a larger area but draw the enemy's attention to that spot.
Overall, this was pretty cool and effective for how simple it is!