When they respond Apple changes policy for EU users, not for anyone else.

Already users based in the European Union with an iPhone have the ability to install apps using alternative app marketplaces or web distribution, in addition to the App Store.

Is that so? I’ve been waiting to try app sideloading but haven’t seen any app repositories or so that work with the app marketplace APIs

Yes. It has been just few months. It takes some time to catch up.

Mobivention (b2b specialized) https://app-marketplace.eu/

AltStore https://altstore.io/#Downloads

Sometime in the future, Epic Games Store, MacPaw’s Setapp