Getting started as an alternative app marketplace in the European Union
developer.apple.com
developer.apple.com
This is not going to happen. "Pay us fifty cents per user per year, forever, for the privilege of competing with us" is a joke, it will not be tolerated by EU regulators.
I feel less certain about the CTF charged to app developers, but the CTF applied to marketplaces is flagrantly anti-competitive.
Totally rules out something like F-Droid.