Yes, it is powered. If related, the pi 4 will not power fully off to allow rebooting with the powered 6 TB drive attached.
As a workaround, with the usb stick (non m.2) - to reboot I used ‘poweroff’, then an ewelink plug to kill power (to both the pi 4 and the 6 TB drive). Upon turning the plug back on, the pi 4 would boot OK and the 6 TB would be mounted.
This is not the case for the m.2 boot - as the 6 TB being present prevents boot.
My point I was trying to make is you are mixing up the PARTUUID= with the UUID= as specified with the command sudo blkid /dev/device#. The print out is as the system see’s your device.
You can use LABEL=??? or UUID=??? or PARTUUID=??? but use their values as your system goes by. Don’t try to swap one value for another.
Notice the PARTUUID=b75fdbb1-02 value is in a different shorter format than the UUID= one. You had specified UUID= values in the PARTUUID= line in your fstab which does not exist.
Firstly - I’d like to thank you for all the help you’ve given over the years in the archlinux forum. Sometimes to me directly, but often to someone who had the same issue as I had.
Secondly, while I understand it looks like a UUID I think it’s a PARTUID:
By the way, if I plug in the 6 TB to a booted pi4, I get I/O errors /usr/bin/ls not recognised etc, and need to unplug the pi4. At this point I’m thinking to set the 6 TB up on a NAS and point to that. Cheers!