FYI you don’t have to run Graphene or Calyx to be able to side load apps on Android. Just use F-Droid or download APKs out of band.
Discussion
Don't use F-droid. Use Obtainium. F-Droid is as centralized as the play store, but with different rules.
Stock Android is pretty googlefied but they don’t currently limit you to their App Store at least.
Anyone needing to hear that won't understand it.
Translation: you don't have to use the mainstream app store on Android to install your apps. You can install a third-party store, like f-droid or obtainium, or you can actually download and install your app directly onto your device like on a computer (apk is the extension of android applications).