https://www.fsf.org/news/2010-05-app-store-compliance
Maybe? Might have changed since then.
https://opensource.stackexchange.com/questions/9500/is-apple...
One could imagine that if the platform was opened to side-loading, the first third party app store to gain popularity would not be one from Meta or Google, but an F-Droid analogue for FOSS hobbyists and purists.