When I was talking to my daughter about air gestures she geeked out that it could be like using a wand in Harry Potter. She said you could use the gestures in the game Harry Potter: Wizards Unite for the various functions? The ones she used as examples were "Lumos" which would turn on the flashlight, "Avada Kedavra" to turn off the phone or "Alohomora" to unlock it. Anyway, she was incredibly excited about the possibility of something like these working with the S-Pen. I have to imagine others would go nuts for it as well. As to what gestures to associate with them I don't know but this may help
https://www.ign.com/wikis/harry-potter-wizards-unite/Spell_List
Other than that, think of common tasks that are in a variety of apps (copy, paste, open, close, play, pause, skip) and create gestures for those to start with. They will by far be the most used and useful.