Some Arch packages have been rebuilt and resigned by more trusted PGP keys. Those packages are not currently installable on Manjaro. Leading to:
error: swappy: signature from "Maxim Baz <firstname.lastname@example.org>" is marginal trust :: File /var/cache/pacman/pkg/swappy-1.4.0-1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)). Do you want to delete it? [Y/n]
The list of packages is here.
Not entirely sure be done on the Manjaro side, perhaps resyncing with the updated / newly signed packages.