I agree it's not the appropriate response. Someone should report it upstream.

@einpoklum, it's a little bit interesting that you on the one hand make your system be part of Devuan's (and thus Debian's) testing/unstable effort and on the other seem annoyed that not all of that software is fully integrated as a stable release environment with "complete organisational branding".

Whilst it's helpful that you unravel misbehaviour, I'd suggest that your annoyance is somewhat misplaced. Rather one would expect you to follow through on the priviiege of partaking in the trialing of testing/unstable software by reporting on the feedback channels set up for that purpose. You have isolated a functional misbehaviour which thus should be reported to the upstream maintainers (those concerned with the functionality rather than packaging).

Also as you probably are aware, Devuan's charter is to reflect Debian sans [identified badness], and there is no additional commitment to software interoperability and completeness. It obviously would have been fun if that software (apt-add-repository) had been designed to automatically slot in a Devuan branding (or arbitrary non-Debian branding) in its principal functionality, but extending that software (either specifically for Devuan or generically in its design) is unrelated to [identified badness] and therefore actually outside the scope of Devuan's charter.

But there's of course nothing wrong in pointing to these kinds of bugs. It's just the matter of following throw with constructive action rather than "whine about it".

That looks well equipped and farily normal. Though  is that only USB 3 ports? Maybe that's a problem for the installer preamble ... I guess your DVD attempt was via a USB drive as well?

If you would have a USB 2 hub it could possibly make a difference; to let the preamble find the ISO and switch into the installer proper.

Alternatively if you could dd the ISO onto an nvme partition to be available there for the preamble's media detection. That would be an option too ... you would boot from the USB stick but let it find the duly labelled nvme partition as its media (for unpacking the installer proper), and when the installer proper has started you could (with immediate Alt-F2 hands-on) guide its media detection to the USB. If you would want that, e.g. to make that nvme partition avaiable for the installation. (If you wish I could give a more detailed step-by-step for this)

Can you provide output of

blkid $USBDEV

where $USBDEV is the device node for that USB; It appears the boot preamble fails to find a duly labelled partition.

Next, if you are somewhat confident with command line, you could try adding EMERG to the boot line (push TAB, then type EMERGE, then  Enter). That will bring you to a busybox shell early in the preamble, where you could investigate things, and especially modprobe any special modules that might be needed for the hardware. When you exit that shell, it will continue with the installation (loading device modules and scanning for the labelled partition).

There's also the variant adding "emerg" in lowercase, which enters the shell late in the preamble sequence (after failing to mount the ISO). At that point it has loaded modules to handle devices, and you might there be able to coax it manually by setting up a loop mount and run unpack by hand... review its /init for inspiration.

... and to continue on the real X discussion; I note that xserver-xorg-core is already a forked package. Though not forked from upstream, but rather a fork of debian's project so as to add the libseat extension that provides the seatd alternative to (e)logind for input device mediation.

which upgrades was that?

Some oldish cards or drives can't deal with GPT partition table but need DOS table.

You could check that by trying again with the first card but then make sure to create a DOS table on it before partitioning. (Use expert mode with activated lowest possible priority level, or perhaps use ctrl-f2 shell and fdisk)

There are also usb sticks that don't support boot setup, but they are rare.

Now I'm more confused, because now I also lose the label when I try it, and I'm actually not sure how I could have imagined something else before.

To make it work, you'll rather have to "be clever" and restore the disk image apart from the first sector after having changed the partition table. E.g.

dd if=devuan_daedalus_5.0.1_amd64_netinstall.iso of=/dev/sdg skip=1 seek=1 conv=notrunc

The partition table is really just the last 64 bytes of the first secor, and the bytes before that have not been changed by fdisk. Some bytes in some later sectors have changed though, which amounts to losing the label, The suggested copying will restore those without restoring the partition table.

I apologise for making this so confusing and convoluted.

hmmm fdisk (mine, of package version 2.38.1-5+deb12u3devuan1) doesn't change the signature (despite the warning), and the partition is correctly marked as Empty in the partition table. It further preserves the partition label (DEVUAN501) which is the access detail used by the installer's mounting.

When you plug in the USB (on another linux) without mounting it, what does blkid /dev/sdg and blkid /dev/sdg1 say? I'd expect it to be like

/dev/sdg1: BLOCK_SIZE="2048" UUID="2023-09-14-08-12-43-00" LABEL="DEVUAN501" TYPE="iso9660" PTUUID="0650bbcb" PTTYPE="dos" PARTUUID="0650bbcb-01"

Actually you can run fdisk on the USB stick and change the partition type to 0x0c. I.e., mark it as plain FAT32 instead of EFI (0xef). Then the partition should not be seen as an EFI partition.... and you may further mount the partition somewhere and rename its EFI directory, say to OFF, to further reduce its appearance as EFI partition.

While in fdisk, you may also add another partition for the remaining portion of the USB stick.

I wouldn't try any other partitioning tool since I would fear it may well be too intelligent and eager to be helpful to not destroy the hybrid ISO setup.

note that you also need to follow up with

apt-get dist-upgrade

which, in addition upgrading packages, adds and removes packages according to the dependency network. To quote the man page:

Note that it's never too early to start reading man pages...

The installation ISOs are set up as "Hybrid ISOs". This means that the ISO is a union of two data perspectives: on the one hand the ISO is a single iso9660 filesystem, and on the other hand it's a disk image with two partitions; the first partition spans the whole ISO and the second partition spans a raw image in format FAT32 within that first partition.

It's kind of like this (in beautiful ascii art):

+----------------------------------------+
|              ISO image                 |
|        +-------+    	      	      	 |
|        | fat32 |                       |
|        | image |                       |
|        +-------+                       |
+----------------------------------------+

The iso9660 file format allows for having a DOS partition table in its first 512 bytes, so those two data perspectives blend nicely and leaves it to the device driver to pick and choose which view it adopts. A cdrom drive will adopt the view of a single iso9660, while a disk driver typically adopts the view of 2 partitions (although it's vaguely unhappy about the partitions being overlapping).

The fat32 partition is further marked as an EFI partition so that the disk view makes UEFI more happy because on "the surface" it looks like an ordinary UEFI setup.

BUT it also fools grub's intelligent install logic to make it install grub for UEFI regardless of which bios there is. Probably it just scans the disks to see if there is any EFI partition and from that jumps to the conclusion that the system has UEFI bios.

Therefore you need to exercise some manual hands-on towards the end to explicitly install the grub variant you need. This can be done either after or instead of the installer's grub installation. You where doing it right using the rescue mode.

Secondly, you cannot install linux onto a FAT32 partition because that filesystem type does not have symbolic links. You must format or reformat it into some filesystem type that can.