This finally worked for me
:
source: https://fosstodon.org/@mobian

Code:
curl -s https://repo.mobian.org/mobian.gpg.key | sudo tee /var/lib/extrepo/keys/mobian.asc
source: https://fosstodon.org/@mobian
Using encrypted Mobian (bookworm) on pmOS CE Convergence PinePhone (3GB/32GB) as Daily Driver, and Beta Edition Convergence PinePhone (3GB/32GB) with encrypted Mobian (bookworm) as Backup device.