I'd like to point out how i got mine to work.
I tried installing whatsapp by doing a restore from google, after typing in the email it asked to add account again. When i did it said "already in use".
I gave google play store, google services framework, and google play services permission to contacts via the "apps" app in grapheneos.
gave whatsapp every single permission possible
I went into play store, and logged out of all my google accounts.
went back to whatsapp and entered the google email to restore again, and it worked like a charm.
go back and disable every permission possible that you don't want on those apps.