Why do firmware updates not apply?

I found this troubleshooting guide by the developers of fwupdate which suggests to try to apply updates one by one:

Booting into fwupx64.efi but nothing happens

Are you applying multiple capsules simultaneously? This could mean doing a TPM update and BIOS update at the same time, or an FMP update and BIOS update at the same time. I am doing multiple updates and it fails

1. Re-run the cleanup systemd unit.

   • You'll need to remove a state file (in /var/lib/fwupdate/done or somewhere similar - distro dependent)
   • This removes the payloads from EFI system partition, Boot entries and all NVRAM variables.

2. Re-run just one update at a time. If this fixes your problem, please report an issue with the relevant details.

Following these steps I succeeded to install the system firmware update:

$ sudo fwupdmgr clear-offline
$ sudo fwupdmgr clear-history
$ sudo fwupdmgr install ${HOME}/.cache/fwupdmgr/afddc660b9a0f8045feaa4703f8258a5d197dad1-Signed_1152921504627781711.cab

After a reboot, the DELL system firmware updated itself.

I was not able to also install the TPM firmware upgrade yet. Maybe the troubleshooting guide on how to solve issues with applying a single update helps in debugging the issue and finding enough information for a bug report. I have not tried yet.

I was able to apply the System firmware update by clearing the fwupd history and applying the System firmware update alone.

According to this post, you need to clear the TPM owner information before applying the TPM 2.0 firmware update. But, you may lose access to your files by doing this, so please perform a backup and verify it first.