I enjoyed this, particularly the way that mobility mechanics are unlocked over time. It definitely evoked an older era of FPS, but still managed to present something that felt a little new and unexpected by expressing those sensibilities with some different styles of movement/avoidance challenges.
The first time I got the gun, it stopped working after a few shots, and I needed to restart. I also found it a little difficult to time double jumps properly - I'm guessing that I was doing my "first" jump after leaving platforms. As others have mentioned, I also found air control a bit tricky to work with, but I feel like most of the places where I had troubles were optional spaces that I didn't have to explore (climbing on top of book shelves, etc.).
Hope you had a positive experience using Godot and Qodot for 3D work, and thanks for doing a Linux build!