Comment # 8 on bug 972394 from Matthias Klostermair

Yes, this is required for the access, like so:
## PSD
disk ALL=(ALL) NOPASSWD: /usr/bin/psd-overlay-helper
# Where my user is "disk". 

To see a preview of the in you /$HOME/.config/psd/psd.conf:
$ psd preview


And then to enable the service as user:
$ systemctl --user enable psd
$ systemctl --user start psd

It can load the overlayfs on demand but to be sure it get's loaded you can do:
$ touch /etc/modules-load.d/MODULES_LOADED_ON_BOOT.conf
$ echo overlay > /etc/modules-load.d/MODULES_LOADED_ON_BOOT.conf

I hope you don't mind. I continue providing output tomorrow.