Update error keyring

sudo pacman -Syy
sudo pacman-key --refresh-keys
sudo pacman-key --populate archlinux
sudo pacman -Sc

Or:

sudo rm -r /etc/pacman.d/gnupg
sudo pacman-key --init
sudo pacman-key --populate archlinux 
sudo pacman-key --refresh-keys
sudo pacman -Sy gnupg archlinux-keyring 
sudo pacman -Sc

Source:

• https://forum.manjaro.org/t/manjaro-is-unable-to-update-gpgme-keyring-errors/96941
• Signature is unknown trust - Arch Linux on VBox - DEV Community 👩‍💻👨‍💻