Sure thing, as long as it doesn't require any permissions. I have installed multiple apks on my phone from unknown people. Note that Google's requirement is also for completely permissionless apps like games.
There are about a half dozen permissions that are regularly abused by malware. These permissions are also extremely useful for a ton of completely legitimate features.
I am pretty confident that if Google had enabled this policy only for apps which use these permissions that the community would still be upset.
You won't pass Google Play hardware attestation that way, and you won't find a bank in Europe or the UK that doesn't require that to log on to their website within five years.
My bank works fine after relocking (in NL, Europe). And last time I checked all Dutch banks work. My VISA credit card app (from ICS) also works. Same for the government identification app, the government message app, our insurance app. In fact, I haven't encountered anything outside of Google Pay that didn't work.
(I don't deny that there are apps that won't work. Best to check before switching full-time.)
That's a prediction I would disagree with. Firstly, there are application developers which specifically add support for GrapheneOS if they are asked nicely. Secondly, there is a chance that Play Integrity will have to change due to anti-trust regulation.
You pass basic, but not device or strong integrity. This is purely googles fault and is an artificial limitation that requires regulatory restrictions.
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