> Core Technology Fee — iOS apps distributed from the App Store and/or an alternative app marketplace will pay €0.50 for each first annual install

emphasis added on and/or; it seems like Apple is being forced to break down fees according roughly to their costs (?). Maybe installs from altapp stores cost them some resources because they want to verify the notarization each time?

Apps don’t have to pay for notarization on MacOS, and nobody forces Apple to perform notarization in the first place. It’s also implausible that there would be any notable cost per install.