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1e2j6 for contacts, what I do after I used to get them from Google contact sync when I was newer on GrapheneOS, was of course give Google Play Services the contacts permission, go to setup and restore in Google Settings under Apps, and then restore my contacts. Then remove contacts permission from GPS.
Then I started exporting the .vcf contacts file from settings in the Contacts app, and then importing it again right away. That way it populated the "device" contacts section in the Contacts app! When you get them from Google, they are all marked as "Google contacts" and not "local device contacts."
If you export then import them like this, and get them saved as "device contacts, Seedvault will back them up for you to USB backup when you do an app backup, along with SMS, MMS, System Settings, and Call Logs.
Proton Mail is supposed to have a Contacts function. I've been meaning to try it, since even though its an older feature and I've had Proton Mail since it was announced I've never heard if it until last week! I just searched and found this very helpful article that shows how to take that very same .vcf file that you get when you export the Google Contacts while making them " device contacts" and you can use that to import them all into Proton Contacts (part of Proton Mail) and store them encrypted!
Hope this helps!