[blastersyndrome]

Realistically, what can be done to stop this?

In my eyes, Google is violating my rights because I did not agree to them stopping independent installation. I view them pushing this update as criminal vandalism.

[NotPractical]

A law with more teeth than the EU's Digital Markets Act (which, contrary to popular belief, does not actually require sideloading) could theoretically be passed. The current (pre-lobbying) iteration of the App Store Freedom Act looks pretty good (ctrl+f "security", "safety", "integrity" returns zero results).

https://www.congress.gov/bill/119th-congress/house-bill/3209...

Realistically speaking, that probably won't happen, though. What can you, yourself do to mitigate the impact?

Install a forked version of Android without Developer Verification. LineageOS, GrapheneOS and CalxyOS are all pretty good options. Stop using any apps with remote attestation via Play Integrity, which will mean sacrificing more and more functionality as time goes on. Try to use mobile sites instead of mobile apps as much as possible. Watch the F-Droid catalog get smaller and smaller until it crumbles completely when it becomes unusable by >80% of Android users.