Fantastic game! It's so wonderful seeing something inspired by Myst. I love the atmosphere, how each level sounds distinct and how the sound matches the visuals and even how it gets more heavenly up top for instance. I LOVE the voice of Aeternum and how it's timbre changes depending on the range, where down low, for instance, you can hear a nice crackling in the voice. The puzzles weren't too hard but satisfying and they definitely felt like they fit perfectly with Myst.
That said, I did have a few problems. I understood what you had to do to open the door but on the 2 times I tried it I opened it as I was tinkering with it without exactly knowing I had done it. Only on my second time opening it, after the fact, did I understand how it was supposed to look for it to open. Could very well just be me not being very good at this though but, either way, I thought it could be useful information for you to have.
I also found a bug playing the first time yesterday where the paths of the cars weren't playing all the steps you find on the paper or even starting from the beginning so I thought any set of instructions could have a decent bit of shared movement and you had to find one small discrepancy based on a small amount of information to know which car is following each set of instruction and maybe later you'd figure out the rest of the path based on the layout of the map or something. It didn't help that the set of moves on my first go were similar. This time around the moves were much more different from each other and the monitor was playing correctly at which point the puzzle became so much simpler than what I had imagined.
The movement could be a little tricky at times but not that much of an issue. I could always get to where I wanted, it just usually took a few more clicks than desired. Some screens turn you to the right even though you clicked left for instance but, once again, not too big of a deal. I really like the subtle way the game tells you there's a screen on the right, for example, with just a gentle glow when you hover the mouse though. I found that helped to keep the atmosphere while being helpful to the player.
I liked the music puzzle, I always like when games have music puzzles, and it's nice that the answers to the puzzles are always different. And in regards to the music puzzle itself, I really like that there's a different melody and it's not just the same melody with a different note missing.
The bit of worldbuilding with Aeternum was also a nice touch.
Great game! Enjoyed it quite a bit. Would love to play a longer version for sure. Congratulations.