I just tried this AUR package: AUR (en) - systemd-guest-user
Test was on Manjaro XFCE in a VM.
pamac build systemd-guest-user
reboot
Login with user “Guest” without a password and you are good. That is the best setup I’ve seen in the wild.
Source: GitHub - Akrai/systemd-guest-user: A simple systemd configurations for guest user support
It create a tmpfs for Guest so that anything written to /home/guest will be stored only on the RAM and will be lost on a reboot.