When the device is busy, it’s been utilized. Reboot your computer and it should no longer be in use. I had to retry the installation of the cab file a few times get it to flash.
Use the EFI USB method to update your BIOS firmware, personally could not do it with fwupd and fwupd maintainers seem to be aware of that problem. If you want to help them out before updating, checkout this issue on their Github : Failed to connect to daemon · Issue #6308 · fwupd/fwupd · GitHub