Comment # 40 on bug 1203748 from Stefan Dirsch

(In reply to Giovanni Gherdovich from comment #39)
> To recap: your system is legacy BIOS, 

Yes, kind of, i.e. openSUSE Leap 15.3 was still using legacy BIOS for
installation, in more detail.
It runs on CSM mode, i.e. the legacy BIOS compatibily layer on top of UEFI. At
least that's how
I understood it.

> the vendor offers BIOS updates only
> via UEFI capsules and their only documented update method is with the Linux
> tool fwupdate(1). fwupdate doesn't work if the system uses legacy mode. So
> what you did is use a (uefi) live image from a USB disk with fwupdate, run
> the update, and then continue use legacy mode on an update firmware. Am I
> getting this right?

Yes, in legacy BIOS compatibility mode CSM. See above.

> This kind of shows that there is only one firmware; I somehow always assumed
> there are two, one legacy and one uefi. But apparently you're always running
> the uefi BIOS, only it has a thin compatibility layer on top so you can keep
> using the old interface. Does that make sense?

Yes, definitely. Only one (UEFI) BIOS. Well, in more detail. It was first
installed an update for
ECP (Embedded Controller Program) . On top of that the update for the UEFI BIOS
(first step to an intermediate version).
Then another update for UEFI BIOS (second and last step to the final version). 
For all these a boot entry was generated and
the update didn't happen before selecting this boot entry.

Then also the firmware for the NVME has been updated. This happened
immediately.