Why can't I upgrade firmware on my Thinkpad after upgrade from 20.04 to 20.10?
I found the solution to this problem: For some reason a package called 'fwupd-signed' was not installed in 20.10 but must have been on 20.04 since I was able to upgrade firmware without problems. So the upgrade process from 20.04 to 20.10 left me without this package needed for firmware updates.
Run the command apt install fwupd-signed and try install again.