I guess it would work, too. Never done it myself...

If I may interject my basic dumb conceptual question here:
Is there any advantage to using EFI,
as opposed to switching bios to legacy/csm mode?
(Thanks and please excuse my interruption)

There are pros and cons to using FEI over legacy mode. Its your choice.

Pros, EFI expects drive partitoning done with GPT. This allows form many more partitions than MBR ( legacy ) partitoning. Many new drives are available in over 2T bytes, I think this is the point you need GPT, if youwant to use all the drive space.

Cons, if you have an install running on MBR, and want to use EFI, there is some work to do. Regpartitiong to GPT, formatting, and reinstall. There is a learning curve as well. You need a FAT partition to boot from, this is added on conversion from MBR to GPT. You need to learn how to maintain the efi partition with kernel upgrades.

Other things to consider, eventually, manufacturers will make the CSM module disappear, on some products that has already happened. So, ask yourself, do you want to migrate now, or be forced to it later when you get a new hardware that only supports UEFI? Your choice.

A system installed on MBR will run well on the CSM modules supplied my most manufacturers, so no need for action right now.

In a way this thread is no longer relevant. I have reinstalled again.

Facing the "Install LILO" screen. Well, with a 64-bit UEFI-system, I don't want LILO but rather ELILO.

So, Do I pick simple, expert or skip?

As it is, I did look into expert, but then exited, hoping to be able fix things after the install process finished. As yet, I've not rebooted. Staring at the #

Maybe noteworthy to mention: On nvme0/n1p0 I have boot/efi. Or at least should have. It was set up in the first functioning install. Like the swap, it didn't show up as I chose nvme0n1p3 to be /.

I only have three partitions and those are /, /home (not formatted) and nvme1 as a filedump (not formatted) so boot ought to be under the (quick)formatted /.

to use efi, when you partition your disk before running setup, you need to create an efi partition -- doesn't have to be large, because it will just hold the kernel, and maybe the previous kernel, if you want to keep it to go back to in event of new kernel failure... and also if you are dual booting it would hold other os kernels... I don't dual boot, and 100MB has been adequate. When making the partition, be sure to set the type to efi. In gdisk, that is type ef00. Once that efi partition is present, the installer will pick it up and ask if you want to install elilo during setup.