If you look something like :
error: freeplane: signature from "Leonidas Spyropoulos <artafinde@archlinux.org>" is marginal trust
:: File /var/cache/pacman/pkg/freeplane-1.9.12-1-any.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
You should update keys:
sudo pacman -Sy archlinux-keyring
https://wiki.archlinux.org/title/Pacman/Package_signing#Upgrade_system_regularly