Ahhh! The tab thing would help a lot. I really think it would be worth noting down the controls in the game description: I appreciate you don't want to give anything away about the story, but I don't know how many people will work out how to play just by trial and error.
I'll definitely look into that feature of Godot. So far I've only just started working my way through an FPS tutorial (since that's the main thing I can't make using other tools I'm more familiar with). Something like this could actually be a good middle ground: same as you, I'm much more familiar with web and mobile stuff.