The goal in the demo is not to find and solve 100% of everything accessible. I made that more clear in the latest versions. With the amount of queries you have solved you have done something akin to beating the demo on hard mode. It's not required of any player but it's still there for players who want to try out how far they can get. The museum interior and garden shed are not accessible.
I'm very happy to hear you understood how the game communicates with the player and you did a great job at recognizing that some of the tools and mechanics are never directly pointed out to the player. There are nudges here and there but some ways of interacting with the game are not immediately obvious and reward the player for figuring them out.
The car trunk was not intended to be a secret but since it's not directly mandatory for the demo I overlooked that nothing points to checking it out.
even though I found flower petals in the apartment and in the park, and I spoke about it with the wife, the compendium didn't let me look for a rapid aging page.
If some supernatural principle doesn't have a corresponding entry you can safely assume it's a theory and not a previously encountered phenomenon. Not everything supernatural will have an immediately relevant Field Studies entry. The dialogue points out it's speculation.
The Gabriel Knight 3 comparison is an amazing compliment.
A lot of the leftover rough edges in the gameplay experience (dialogue system mostly) should be smoothed out by the time the game is finished.
If you enjoyed the demo consider leaving a rating on the itch.io page. I appreciate the feedback and the supportive words.