[summm]

Nope. It is still not possible to give someone else (the government, or the bank) control over your phone while at the same time run software that you alone control with higher privileges. Please don't mix that up with "is practically hard to implement because of sloppy code. Also your attacker model is still "occasional evil government agency or evil private corporation wants to crack and read your messages", while what is discussed here is more fundamental "evil government or abusive corporation controls your phone in the first place, and can just remote control it you can't use really secure apps"

[whazor]

I want governments and banks to allow open-source software, not control my phone.

For example, I essentially trust the ROM I download from the GrapheneOS website. What I want is for governments, banks, or some independent open foundation to be able to approve that ROM too, so attestation can work with it.

More like how CA certificates work: not perfect, but not locked to one vendor either.

[summm]

So now you have the choice between two approved ROMs. Not a lot of improvement? And as soon as GrapheneOS implements something beneficial to the users that the government does not like, the approval will be taken back. That's also why GrapheneOS will probably not even think about doing that. So you want some OS functionality neither Google nor Graphene offer, you're, again, out of luck. CA is something completely different, and much more limited in what can be centrally controlled. Everybody can go to a CA, get a certificate for their domain, and use it with any server software, even with software they compiled themselves.