You need to remove this then.
sudo pacman -Rns WallpaperEngine_kde6
You need to fix your keys then.
You can do something like the following;
sudo cachyos-rate-mirrors
sudo rm -r /etc/pacman.d/gnupg/
sudo pacman-key --init
sudo pacman-key --populate
pacman-key --recv-keys F3B607488DB35A47 --keyserver keyserver.ubuntu.com
pacman-key --lsign-key F3B607488DB35A47
sudo pacman -Scc
sudo rm -r /var/lib/pacman/sync
sudo pacman -Syy archlinux-keyring cachyos-keyring
You probably did not need all of it but this covers just about everything that could be wrong with the keys I think.
You might consider upgrading a little more frequently in the future and/or dont let things get all messy.
Then how does an upgrade go?
sudo pacman -Syu