I’m going to guess that if you run (as root):
fwupdmgr update
You’ll see something like this:
# fwupdmgr update
╔══════════════════════════════════════════════════════════════════════════════╗
║ Upgrade UEFI dbx from 371 to 20241101? ║
╠══════════════════════════════════════════════════════════════════════════════╣
║ This updates the list of forbidden signatures (the "dbx") to the latest ║
║ release from Microsoft. ║
║ ║
║ An insecure version of Howyar's SysReturn software was added, due to a ║
║ security vulnerability that allowed an attacker to bypass UEFI Secure Boot. ║
║ ║
╚══════════════════════════════════════════════════════════════════════════════╝
Perform operation? [Y|n]: Y
Writing… [ ]
failed to write-firmware: failed to write data to efivarsfs: Error writing to file descriptor: No space left on device
If that’s the case, then you need to go into your EFI BIOS and reset the certificate database to the default. You probably will want to disable secure boot while doing this (just in case a signed module’s certificate isn’t in the stock database on your system).
How you do that will depend on the BIOS - you’ll need to check the manufacturer’s documentation.
Once that’s done, you should be able to run the fwupdmgr command again.