Hoo boy. That was a rollercoaster ride. Where to start.
This is going to be a long comment.
1. Yes they can. In fact, I think they do already, as is! What you have here is a kitschy masterpiece. I am honestly in disbelief that you made something this offbeat, thought-through, and sizable in a month with no prior GameMaker experience.
2. This game is not only well-paced, it uses pace in really interesting ways. When you first play through the levels, they're a tad basic - restrictive in structure and discouraging momentum, never getting that complex. But when the game finally shows that it's doing the NieR thing of revealing further depth of gameplay and plot later on, you're on the edge of your seat and really get into the zone. It actually helps that the standard levels aren't that challenging, because it makes the second playthrough when searching for the secret area a quicker and more contemplative experience. Then, right as your expectations are completely set up for more rote combinations of lasers or red tiles, the game throws a creative curveball at you, every single time.
3. The music choices definitely work well. I actually think this game's use of pre-existing assets helps it subvert expectations and create its own bizarre aesthetic, and the music really helps with that, in addition to fitting the tone in the moment.
4. The hints are generally good, but I'd change the "look for a light in the darkness" to "look for a light in the darkness above" to make things a bit easier to infer. I actually had to use the walkthrough to get past that riddle.
5. Words fail me. I started out thinking this was yet another GameMaker game, yet another itch game, something I'd play for five minutes and get bored of, but the strange wonder of the game's world and gameplay made me see it through to the end in one sitting. There are some typos, a few glitches, and the writing can get unnecessarily sesquipedalian at times, but this game is a far sight better than I expected (especially for something made in such a short time). Even the name, "A Proof of Concept", adds a lot to the experience.
It's amazing that something this cool could come out of quarantine. This is one of the best itch games I've ever played, and it runs well even on my crappy computer. Thank you so much.
Edit: I also like how you can play the endgame levels on the first run if you know what you're doing.