Currently looking at this post: Error 94, I/O Error
Looks very similar to my problem. He suggests installing usbguard:
sudo apt install usbguard
Which I will try now, BUT, on the whonix-workstation-18 template, the same packages is NOT installed, and YET, attaching the same bluetooth to whonix qubes works. Why would it work without needing usbguard on whonix qubes then?