I really appreciated the look and smoothness of the main character's animation in this one. Unfortunately, I didn't actually know the game had upgrades until I came here and looked at the page after I had reached the end. The levels also included a couple of "leaps of faith" requiring the player to just trust that they would land reliably since the camera was too zoomed in to see what would happen.
Good work though, I think with some polish and a bit of research into some of the really good resources we have for side-scrolling platformers in Godot, you have a great jumping off point. I recommend looking into GDQuest if haven't already, it's made by the devs and they're actually covering how to do side scrollers with best practices currently. There are always a ton of great free resources available too!