Apple allows alternative marketplaces on iOS in the EU.

Alternative app marketplaces are unique kinds of iOS apps that you can use to install other apps on your iPhone. You might alternatively be able to download an app directly from a developer’s website through web distribution. Alternative app marketplaces and web distribution can be used in addition to the App Store. Users in the European Union can install an alternative app marketplace on iPhone by downloading it directly from the website of the alternative app marketplace developer.

https://support.apple.com/en-us/118110#:~:text=Alternative app marketplaces and web,the alternative app marketplace developer.