The command that worked for me was this:
sudo usermod -a -G uucp $(whoami)
Followed by a reboot. Logging out might work too, and hopefully someone sharper than I am will come along and enlighten us all on how to effect this without needing to reboot or logout. I tried running
newgrp uucp
but was still unable to connect. After rebooting (and having a moment when on first boot
/boot/efi was not found, but it worked on a subsequent reboot), I am able to connect to the LED spacers.
I hope this helps.Have a great day!
Edit to add tagging @DRACONIUM
Edited again to note - updating the fstab to use the uuid for the /boot/efi partition rather than /dev/nvme1n1p1 seems to have resolved things, Noted for future setups. This may be obvious to more savvy users, and something in the back of my mind is saying that I have run across it previously, but this time I wrote it down. Maybe one day when I grow up I can be a real boy.