Unfortunately American culture is simply unsuited for free expression unless buttressed by something list the 1st amendment, which of course only applies to Government.
Fundamentally Apple can and will do whatever it wants and there is no point complaining to them. OTOH allowing direct installs and multiple apps stores is a security disaster. But parliaments can pass laws to regulate monopoly conduct, in the same way that essential services are. Privacy, competition policy (including market access), arbitration procedures for small vs large companies, etc are all mature fields of law, and action in any large market would have significant effect on Apple/Google policy.
Lobby your politicians. Support organizations like EFF.
[1] https://www.usenix.org/system/files/login/articles/login_dec...