It would probably be helpful to see the actual lines you added to /etc/fstab.

If you installed Cinnamon desktop using the excalibur 6.1.1 iso set, attempts to have some kind of sound working after installation.  Sorry it didn't work out for you.  The installer creates /etc/xdg/autostart/pipewire.desktop file that attempts to run daemon to start pipewire, pipewire-pulse, and wireplumber.  Since this method isn't working on your system, before attempting other ways of getting these processes to start up, you should first disable the xdg autostart.  You can do this in the Cinnamon GUI: Menu -> System Settings -> Startup Applications, turn the slider for Pipewire to the off position.  Then you may try other methods of starting pipewire, if that's what you want to use.

There's a devuan excalibur grub2-efi netinstall iso at https://files.devuan.org/user/tempforever/
I haven't tested it extensively but it might work in those rare cases that syslinux doesn't work.

OK, you found the solution

On daedalus, I just use xsane
Not sure what driver it uses.
it reports: Loaded backend: hp3900:libusb:005

Is the arm system already up and running when you plug in the screen?
If so, try shutting it off, plug in the screen, then power the system back on.  Does anything come on the display screen now?

The config.txt file should be in /boot directory.

There's an issue with the current freia netinstall iso.  It's not booting in virtualbox with efi enabled.  Haven't tested it on actual hardware yet.  I was going to wait until I addressed that, but since there's evidently a demand for it, the netinstall is back and should hit the iso mirrors shortly.

[edit]
the current state of freia installer is not good.  download and test if you'd like, but for me it's now failing at the step Partition Disks and will not proceed (even if run /usr/bin/partman).  Hopefully this will be fixed soon.

I don't use tailscale myself, but was trying to help a friend who is on excalibur.  I pointed him to https://github.com/tailscale/tailscale/issues/9502 and he was able to get it working (with sysvinit).  There's a sample init script (or two) down in the thread.  I'm not sure exactly what he went with.

ComputerBob: If you still are having troubles after trying any of the proposed solutions, please post the exact output of the commands you are running.  It's hard to guess what went wrong without a specific error message, and I'm not even sure what you were trying to do in the first place.  Is apt update giving an error?  The more information you're able to provide, the more likely it is that someone will be able to give helpful steps to fix the problem.

I wrote a script to fix plasma-discover problem.  I'll try to integrate it into the installer soon.
I used this post as a starting-point: https://dev1galaxy.org/viewtopic.php?pid=41726#p41726 but had to change a few things.  These pages were helpful references: https://www.freedesktop.org/software/ap … -YAML.html and https://www.freedesktop.org/software/ap … Cache.html
Anyway, here's the script that should get plasma-discover working on devuan excalibur.  If you need it on different devuan version, it shouldn't be too difficult to adjust.  Also, you'll need write access to /var/lib/swcatalog/  so you'll probably want to run it as root.

#!/bin/bash

# create target directory
mkdir -p /var/lib/swcatalog/yaml/
cd /var/lib/swcatalog/yaml/

# download components
for suite in excalibur excalibur-updates excalibur-backports; do
  debsuite=$(echo $suite|sed -e 's/excalibur/trixie/g')
  for component in main contrib non-free non-free-firmware; do
    echo "Downloading: component: ${suite}-${component}..."
    wget -q https://appstream.debian.org/data/${debsuite}/${component}/Components-amd64.yml.gz -O devuan-${suite}-${component}_amd64.yml.gz
  done
done

echo "Patching component: excalibur-main_amd64 ..."
gunzip devuan-excalibur-main_amd64.yml.gz
lstart=$(grep -n ^Type:\ operating-system devuan-excalibur-main_amd64.yml | cut -d : -f 1)
lcount=$(tail -n +${lstart} devuan-excalibur-main_amd64.yml | grep -n ^---$ | head -n 1 | cut -d : -f 1)
lresume=$((lstart + lcount))
head -n ${lstart} devuan-excalibur-main_amd64.yml > devuan-excalibur-main_amd64.tmp
cat <<HERE >>devuan-excalibur-main_amd64.tmp
ID: org.devuan.devuan
Name:
  C: Devuan GNU/Linux
Summary:
  C: The universal operating system
Description:
  C: >-
    <p>
      Devuan is a free operating system (OS) for your computer.
      An operating system is the set of basic programs and utilities that make your computer run.
    </p>
    <p>
      Devuan is based on the Debian project, but with a focus on init freedom.
    </p>
Developer:
  id: org.devuan
  name:
    C: The Devuan Project
Url:
  homepage: https://www.devuan.org/
Icon:
  cached:
  - name: devuan-logo.png
    width: 48
    height: 48
  - name: devuan-logo.png
    width: 64
    height: 64
  - name: devuan-logo.png
    width: 128
    height: 128
Releases:
- version: "7"
  type: development
  description:
    C: >-
      <p>The current development version of Devuan, codename freia.</p>
- version: "6"
  type: stable
  description:
    C: >-
      <p>The current stable version of Devuan, codename excalibur.</p>
- version: "5"
  type: oldstable
  description:
    C: >-
      <p>The oldstable version of Devuan, codename daedalus.</p>
- version: "4"
  type: oldoldstable
  description:
    C: >-
      <p>The oldoldstable version of Devuan, codename chimaera.</p>
---
HERE
tail -n +${lresume} devuan-excalibur-main_amd64.yml >> devuan-excalibur-main_amd64.tmp
mv devuan-excalibur-main_amd64.yml devuan-excalibur-main_amd64.yml~
mv devuan-excalibur-main_amd64.tmp devuan-excalibur-main_amd64.yml
gzip -f devuan-excalibur-main_amd64.yml

# download icons
for suite in excalibur excalibur-updates excalibur-backports; do
  debsuite=$(echo $suite|sed -e 's/excalibur/trixie/g')
  for component in main contrib non-free non-free-firmware; do
    for size in 48x48 64x64 128x128; do
      echo "Downloading ${size} icons for ${suite}-${component}..."
      mkdir -p /var/lib/swcatalog/icons/debian-${debsuite}-${component}/${size}
      cd /var/lib/swcatalog/icons/debian-${debsuite}-${component}/${size}
      wget -q https://appstream.debian.org/data/${debsuite}/${component}/icons-${size}.tar.gz
      tar xf icons-${size}.tar.gz
      mkdir -p /var/lib/swcatalog/icons/debian-${debsuite}-${component}/${size}@2
      cd /var/lib/swcatalog/icons/debian-${debsuite}-${component}/${size}@2
      wget -q https://appstream.debian.org/data/${debsuite}/${component}/icons-${size}@2.tar.gz
      tar xf icons-${size}@2.tar.gz
    done
  done
done

I see in slim.conf: default_path        /usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
but I'm not seeing anything similar in lightdm.conf.

Evidently, TTY login gets path from /etc/profile, then ~/.profile - both of which seem to be ignored by lightdm

I know it's not answering your questions (I don't know the answers), but for now you could use a combination of /etc/profile (for tty) and ~/.xsessionrc (for X)

(edit)
From this page https://wiki.archlinux.org/title/LightDM

I was not able to get xprofile to work, either.  I'm wondering if something is missing or misconfigured by default, or if this is a bug.

That should have enabled tty2-6.  Maybe verify some things first:
1. Does the directory /etc/sv/  contain subdirectories named getty-tty1, getty-tty2, getty-tty3, getty-tty4, getty-tty5, and getty-tty6 (among others)?
2. Did the command create links in /etc/service/ named getty-tty2, getty-tty3, getty-tty4, getty-tty5, getty-tty6?
3. Do tty 2 through 6 still show a blank screen with a cursor, and no login prompt?

[Edit]
An easier fix might be just to reinstall the getty-run package.  It should create everything that's needed for runit. 

apt reinstall getty-run

It seems that on devuan, to get tty2-6, runit requires a little bit of manual setup.

ln -s /etc/sv/getty-tty[2-6] /etc/service/

Note that tty1 *should* be working by default, though, as well as switching back to the gui on tty7. So you may have another issue going on also.