In ArchLinux, this is what happens too often when you're running simple upgrade with pacman -Syu:
error: libcap: signature from "-an-author-" is marginal trust
:: File /var/cache/pacman/pkg/-a-package-.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] y
error: failed to commit transaction (invalid or corrupted package)
Errors occurred, no packages were upgraded.
This error has occurred multiple times since ever and by googling, it has a simple solution. Looks like the solution went sour at some point. Deleting obscure directories and running pacman-key --init and pacman-key --populate archlinux won't do the trick. I tried that fix, multiple times. Exactly same error will be emitted.
Correct way of fixing the problem is running following sequence (as root):