Apple recently announces that they will support Alternative App Marketplace where users in the EU can install apps from somewhere other than the Apple App Store.
Other companies such as Steam, Epic, Meta, Google, Spotify, Microsoft might be interested in using this option to distribute their apps. It is not mandatory and an alternative marketplace requires the app distributor to pay a different set of fees compared to the Apple App Store.
This question will resolve to how many marketplaces will be launched by the end of July 2024. I do not live in the EU and will try to get the most correct number based on news sources, social media, and company announcements.
The policy is going to come into effect in March 2024.
Any questions please let me know in the comments.