Having to pay Apple any amount for distributing apps not on their app store is just rediculous. Apple is not curating or providing support for the app in any way.
App developers don’t have to pay the OS developer for any other OS (including Apple with macOS and Google with Android) to distribute apps on their website; why should it be any different with iOS? 50 cents per user per year, along with the same from the app distribution network means that indie developers will be forced to monitize their apps if they have any desire to distribute a sideloaded app on iOS, and the only ones who will be able to run alternative app stores are large companies with the capitol to do so.
Apple wants to dip their fingers where they don’t belong. This is complying with the EU regulation in bad faith.
Also on top of that, the same fee applies on Apple’s App Store as well.