netinstall and a LAN cable should be fine.

When Bookworm shows the resolution of your monitor, there is no reason Chimaera or Daedalus shouldn't. Debian and Devuan share kernel, firmware and most software. Low resolution is mostly due to non-free firmware missing, in this case firmware-amd-graphics.

When trying again make sure the sources.list looks like this one:

deb http://deb.devuan.org/merged chimaera          main contrib non-free
deb http://deb.devuan.org/merged chimaera-updates  main contrib non-free
deb http://deb.devuan.org/merged chimaera-security main contrib non-free

Use apt list to find out if this firmware-package is installed.

I do own such an old mainboard based PC. Got it working alright with Chimaera, legacy install with onboard graphics and a 1920x1200 monitor. The PC is sitting somewhere in a corner in my basement, not being used very often.
I guess Daedalus should also work on such hardware.

There seems to be a problem for as well Debian 12 isos (not the life ones) as for Devuan isos to get it to work in efi mode in the vbox. You end up eithe in a grey screen or some sort of kernel dump saying something about cannot open display. Same problem discussed in the German Debian Forum, also a thread open in the Virtualbox forum, and  bug report 1036310 open against Debian.

Something along the line has changed in the way the graphics is setup between about Nov last year and before.

The main page https://www.devuan.org/ still shows the Devuan 4/Chimaera based information.

To make sure: you have not assigned a password to the encrypted /home as first step?

There is an option to cryptsetup named luksAddKey. With this option you can add further keys (either passwords or keyfiles) but this will ask for an already existing key. I have always used a passphrase as first key, and have no idea how to add a key with a keyfile as only option.

First of all you should correct the fourth line to also read:

deb http://deb.devuan.org/merged daedalus-proposed-updates main

Since Daedalus isn't released yet, I would uncomment this line for the time being.

The rest looks ok, at least for amd64 it works.

I assume you have installed Chimaera = Devuan Stable? Or did you use Daedalus = Devuan Testing?

Devuan kernels are Debian kernels. Generally spoken make sure you have the meta package linux-image-amd64 installed. That makes sure that the latest released kernel is pulled. For Stable you have the choice to add backports as sub-repo, currently on 6.1 kernel. Don't pull in other distros, you will create a Franken Devuan.

The initramfs will be created by the installation post-processing.

Some further information: https://github.com/NixOS/nixpkgs/issues/229450

Sometimes they write nonsense ....

And you should avoid using pkgmaster, use deb.devuan.org.

https://www.devuan.org/os/packages

I think Thunar belongs to XFCE. I am no XFCE user, mine is Cinnamon and Mate. What I can tell is:

When /dev/sda5 is mounted to /delt, you should be able to find the mount point in the file system structure. Open Thunar, then open the File System. There you should see /delt. Try to open. May fail due to access rights.

To your post #5: all devices belong to /root, there is NO way to change rights to other than root.

What you need to do is when  /dev/sda5 is mounted to /delt:
Open a root console, in there:

# lsblk
# df -h 
# cd /delt
# mkdir hans
# chown hans.hans hans

Look at post #15

Replace pkgmaster by deb, then consider if you require the deb-src part. If you are not compiling packages then delete the 3 entries, they are not required.
In addition I suggest to add non-free-firmware (new with Bookworn/Daedalus).