Pretty cool gimmick, It encourages experimentation with the 2 values! This type of game can definitely benefit from secret level exits/collectables littering each level because of all the things you can do when you can control your own gravity and jump! (it'll be cool if in the future there could be enemies/hazards that can also be effected by the gravity slider too!) Problems include there being too many blind jumps, the meters resetting when you die, and the hitbox for the spikes being too big (try giving the spikes a triangle shaped hitbox), I couldn't even find a way to get past that part where you squeeze through that small gap with spikes on the bottom because of their hitboxes, so I just got the highest jump force and lowest gravity and did jumps off the tall wall until I went over it. I also couldn't help but notice that you used the default GDevelop stock platforming template/example game graphics too.
Edit: Oh yeah, the main menu just says "TITLE" instead of the name of the game, and you have to stretch the meaning of the word unstable a bit too much to try to make this game fit the theme for this jam.