Google Ads and Apple's Developer Program.

There are alternatives like mouth to mouth marketing. For developer tools, there's a list (though IDK which of these are European).

There is no European alternative to the App Store or Play Store

This isn't entirely true, you can download them directly from the maker's site. There's places like AltStore, TrollStore, etc. e/OS uses App Lounge, not sure if that's American or not.

Social logins. Your users expect "Sign in with Google" and "Sign in with Apple."

Not all do. I actually feel pushed away by sites that do, as it shows me they don't care about privacy. What should be the common internet practice, is to use a throwaway mail for places you don't often visit, and to use a different mail for places you do more often. Maybe there should be something like a mail manager, à la password manager.

AI

Mistral and Proton Lumo exist. There's also Ollama, Llamafile and Kobold.cpp, those are good AI models. Self-hosting one locally w/o internet connection would be best, but if you don't have that knowledge, the above would also work. Just make sure you don't use the chatbots for anything sensitive. Privacyguides has a good article on this stuff.