You could license it under the (A)GPL, charge for downloads in the Play store or for compiled binaries on ur website and ask for donations on F-Droid.
You could even do a freemium version where some features are locked in the binaries you distribute and need a license from ur website or smth (for those who don’t want to use Google Play). (iirc SD Maid 2/SE does this)
Someone else could just compile the app themselves, unlock all premium features and distribute it to play store without violating the license?
The only thing I still don’t like much about recommending Linux Mint to beginners is that their Cinnamon desktop still uses Xorg which has some horrible display tearing on some Nvidia graphic cards (can be usually fixed with some tinkering and this is akso only my personal experience), which is usually not a thing with Wayland and being Xorg it also means it has inferior touchpad gestures (surely not as smooth as Gnome or KDE) which can be important for notebook users. While being very user friendly it is one of the more resource heavy DE’s I would say even more than Gnome or KDE. It also seems to have some problems with battery life? The official Gnome and KDE desktop packages for Linux Mint are pretty outdated, are still Xorg versions and aren’t officially supported AFAIK (maybe there are some good community maintained packages). Otherwise I agree it’s one of the best choices.