Sadly I never managed to make it to the end of the game, but from as far as I made it (I collected 5 items) I can tell this was a labor of love.
I honestly loved how you did the menu with information just popping up when you hovered over an option. It's very intuitive and looks like it would cut down on having to deal with opening/closing individual windows and submenus. I enjoyed reading the Notes, I'm amazed you've been hacking away on some of these ideas since before I was born! It's cool how past projects from so long ago still have DNA in this game.
I liked how even without voice acting the story comes across fairly naturally through the visual speech and thought bubbles. It's also a very neat diegetic way to teach the player game mechanics, like the nuns talking about how the shadow demon things are warded off with candles.
Each picked up item allowed progression through the game world in a decent metroidvania fashion, and it was kinda cool how each past area changed with each item you gathered.
The only major complaints I have are as someone mentioned some more volume controls, which I notice you said was attempted but were unable to implement fully. I admit thats the sort of thing I usually added last in all of my projects up until very recently, so I know the pain of implementing it.
Also I don't know if it got more obvious, but I wasn't sure exactly what I was supposed to do once I got the bottle of what I assume was holy water. That's the fifth item I collected and where I decided to stop.
I mostly enjoyed what I played, and I admit platformers have never been my personal favourite, so I wouldn't normally play a game like this outside of a jam. That being said I definitely encourage you to continue working on it, there's a decently solid core to it. I would've liked to have the time to try and get all 7 endings but I'm afraid my schedule doesn't allow for it.
Excellent work!