warning: Public keyring not found; have you run 'pacman-key --init'?
downloading required keys...
error: keyring is not writable
error: required key missing from keyring
error: failed to commit transaction (could not find or read file)
Errors occurred, no packages were upgraded.

This is what happened when I ran pacman -S zsh on my new WSL2 install.

I wasted a lot of time trying to fix this thing. I'll jump to the conclusion so you don't have to waste your time too. Entering these (as root) worked for me.

rm -r /etc/pacman.d/gnupg/
pacman-key --init
pacman-key --populate archlinux
pacman -Sc
pacman -Syyu

Read the thread here: bbs.archlinux32.org/viewtopic.php?id=522&am..