I read somewhere that GrapheneOS devs have a strategy which they believe will work -- they strip out something or other about app/device attestation (?) from APK files before installing occurs, or the enforcement code itself from their spin of the OS, so sideloading (ie., user-controlled installation) can still work.
I sure hope so... I think everyone in their respective country needs to scream at their local regulators about this.
Of course, this will only help those whose devices GrapheneOS can run on.