The problem is not only the resolution, I ask also about the resolution in order to get at least a reasonable resolution in the VM.
The biggest problem is that the DE not start at all on real machine and apparently is not of interest to communicate a step-by-step procedure to investigate and solve the issue.

Other OS like Cento (or Gento, I don't remember exactly) also not using 'systemd' have big graphical problems too. On most notebooks are not usable if the user is not cooder or geek.

Maybe Beowulf will start on my hardware if I install XFCE (standard) and add KDE later-on but this is the same as to install Ubuntu with encrypted ZFS-ROOT and install on the top KDE with the result of a kind of Kubuntu (but with all advertisement of Ubuntu on it) with ZFS-encrypted-ROOT. I don't want it!

The other biggest problem is GTK (now announced GTK-4). If someone want an homogeneous DE-UI than is CSD (client-side-decoration) worse and very similar to Windows, Qt use SSD (server-side-decoration). Of course, also under Qt are some apps with hard-cooded appearances.

Lastly I tested Manjaro-KDE that was perfect, all EDID information recognized by default and inserted/reported perfectly in 'xorg', 'xrandir' with the right dimensions, quantity of pixels, etc.. BTW easy installation, rock-solid and all additional software (e.g. motherboard, mouse, keyboard-lighting, printers, etc., etc.) is in the AUR and all in 64-bit. Long story short, all notebooks became this OS, the two big-ones became Arch-KDE.

If you are trying to adjust your HiDPI settings keep in mind that you are probably trying to scale 3 different GUI toolkits: GTK2, GTK3, and Qt5.

GTK2 does not have any builtin HiDPI settings. There are a some pretty good HiDPI hacks that work ok for GTK2 though.
GTK3 applications do NOT scale very well (my opinion). As you have already noted GTK3 will only scale with an integer value. (Correction: GTK3 can scale fonts using a non-integer relative to the currenly set 'GDK SCALE' value.)
QT5 has the best scaling. It will scale to integer or non-integer values.

Here is how I have manually set up the scaling for Qt5 and GTK3 Apps for my 4K Screen.
All of the settings are in my '$HOME/.xsessionrc' since I am currenly using an either JWM or Openbox.

# GTK-3 Scaling
GDK_SCALE=2 export GDK_SCALE                   
GDK_DPI_SCALE=0.5 export GDK_DPI_SCALE 

$ Qt5 Scaling
export QT_AUTO_SCREEN_SCALE_FACTOR=0
export QT_SCREEN_SCALE_FACTOR=2.0
export QT_SCALE_FACTOR=1.9
#

Those settings achive pretty good results.

Here is a good reference: https://wiki.archlinux.org/index.php/HiDPI

Hopefully that addresses some of your concerns.

# Devuan 'backports', 'kernel-' and 'firmware-upgrade' [Link 1:](https://unix.stackexchange.com/questions/545601/how-to-upgrade-the-debian-10-kernel-from-backports-without-recompiling-it-from-s) [Link 2:](https://www.taste-of-it.de/debian-buster-kernel-5-2-aus-backports-installieren/).

**Note-s:**
1. This guide is for people want to get primarily newer drivers for graphic-cards, wifi, etc.
2. The new kernel will be installed alongside the already present-one. In case of problems you can start the "old-one" at boot time.

### Step 1. Detect actual kernel
* For this use `terminal` opening with (CTRL + ALT + T), Code:
```
uname -r
```
### Step 2. Enable 'backports' Code:
* Methode 1.:
```
sudo su

nano /etc/apt/sources.list
```
* Text to insert (leave one empty line at end) Code:
```
# Beowulf-Backports
deb http://packmaster.devuan.org/merged beowulf-backports main contrib non-free
deb-src http://packmaster.devuan.org/merged beowulf-backports main contrib non-free

```
* Save and close file:
 - Save with (CTRL + O), hit (Enter) to confirm
 - Close with (CTRL + X)

* Check results with code:
```
cat /etc/apt/sources.list
```
* Methode 2.:
 - Open Dolphin
 - Navigate to `/etc/apt/`
 - Open `sources.list` with `kate`
 - Copy and paste the 2-3 lines and leave one empty line at end.
 - Save (CTRL + S), insert password and (ENTER).
 - Close with (CTRL + W).

### Step 3. Update and Upgrade
** Note:** You are still `root`!
* read the new sources, Code:
```
apt update

apt -t beowulf-backports upgrade

 > or

apt-get update

apt-get -t beowulf-backports upgrade

apt-get install -f
```
* install `firmware-amd-graphics` (if not yet done), Code:
```
apt install -t beowulf-backports firmware-amd-graphics
```
* install new kernel, Code:
```
apt install -t boewulf-backports linux-image-amd64
```
* search for installed `linux-image`, Code:
```
apt list --installed linux-image*
```
 - output example (note newest installed):
```
Listing... Done
linux-image-4.19.0-10-amd64/stable,now 4.19.132-1 [installed, automatic]
linux-image-5.7.0-0.bpo.2-amd64/stable-backports,now 5.7.10-1~bpo10+1 amd64 [inistalled,automatic]
linux-image-amd64/stable-backports,now 5.7.10-1~bpo10+1 amd64 [installed]
```
* search for correlated `linux-headers`
```
apt search linux-headers-5.7.0*
```
 - output example:
```
Sorting... Done
Full Text Search... Done
linux-headers-5.7.0-0.bpo.2-amd64/stable-backports 5.7.10-1~bpo10+1 amd64
    Header files for Linux 5.7.0-0.bpo.2-amd64

linux-headers-5.7.0-0.bpo.2-cloud-amd64/stable-backports 5.7.10-1~bpo10+1 amd64
    Header files for Linux 5.7.0-0.bpo.2-cloud-amd64

linux-headers-5.7.0-0.bpo.2-commom-amd64/stable-backports 5.7.10-1~bpo10+1 all
    Header files for Linux 5.7.0-0.bpo.2    
```
* install `linux-headers`, Code:
```
apt install -t beowulf-backports linux-headers-5.7.0-0.bpo.2-amd64
```
* install the firmware, Code:
```
sudo apt install -t beowulf-backports firmware-linux firmware-linux-nonfree
```
### Step 4. Assure everything is installed correctly, Code:
```
apt-get update && apt-get upgrade && apt-get install -f && apt-get dist-upgrade && update-grub
```
* in case of error message..., Code:
```
dpkg --configure -a
```
 - alternatively, open `synaptic`-package-manager, click `Edit`, click `Fix Broken Packages`. Repeat the fix until no error-messages appear anymore.

* clean the system (optional), Code:
```
apt autoremove --purge
```
### Step 5. Reboot, Code:
```
reboot

 > or

shutdown -r now
```
* alternatively, use the GUI 
* switch-off command, Code:
```
shutdown -h now
```

The edid on real machine (Kubuntu) is perfect as well on VMs (without 'guest-iso-addition') using systemd, like MX-Linux-KDE and others.
By the way, I install also edid-decode and read-edid, but those apps read the edid-part of /var/log/Xorg.0.log. They don't read the edid from hardware.

I don't know which application read the hardware-edid and pass it to 'Xorg', 'xorg' same?
xrandr work ok, I can set there other resolution's but after a while of running the resolution fall back to 'xorg'-value.

Issuing the command sudo -i systemsettings5 (under all OS) and try to change resolution and scaling belong display-menu I get following out:

kscreen: Requesting missing EDID for outputs (71)

searching for '71' in file-manager I discover /lib/udev/rules.d/71-seat-rules, that's no good.

Reading many threads (for all Gentoo-threads, using and care-taking of 'openrc') about 'kscreen'-errors it appear to be a common error for OSs not using 'systemd' and maybe this is the reason, also for Gento, to issue latest stable without 'openrc'.

I look also for 'EDID' in the real installation (Kubuntu), the file-search don't bring any results but in a gentoo-thread I found where to be, this is /sys/class/drm/, in my case (using display-port-2) /sys/class/drm/card0-DP-2 but there only empty folders and files.

I install also beowulf with 'sysvinit', reading /var/log/Xorg.0.log no changes. This should be also the reason to get black screen with cursor like in a server under real conditions.

A 'step-by-step' instructions how to remedy or how to setup a proper 'xorg' is still missing on my side.

Consideration-s:
1. All OSs using 'systemd' blacklist: 'amd', 'intel' and 'nvidia' modules. How they get all EDID inside 'xorg' is a mistery for me.
2. Mouse, keyboards and thouch-phad are obsolete in 'xorg' (see xorg-wiki).
3. For a 30-40 years old 'xorg' that should be replaced (Wayland and/or + Systemd, maybe) are too few information about and each distribution make own things and place in different folders the config.files. That's not freedom, tha's confusion.

Fact-s:
1. EDID-informations are given by hardware correctly because other ditros recognize them also perfectly even in VM/VB without 'guest-iso'.
2. All firmware (linux and amd) and kernel are up to date from 'beowulf-backports' (see instructions).
3. No seldom hardware, all amd and samsung, see list above.
4. We cannot blame 'openrc', 'syvinit' bring exact the same results= missing resolution-information in the /var/log/Xorg.0.log.
5. Other distro's (e.g. MX-Linux-KDE) recognize available resolution and let modify/change it latest by installing 'kde-full' and use 'sddm' as choosen, devuan don't. This (Devuan) stick with slim at start, does that make a difference? Former installation where the choice was between lightdm and sddm present the same slick slim or lightdm screen.

Have you tried with a more recent kernel from backports "apt -t beowulf-backports linux-image-amd64". And maybe do the same with firmware-amd-graphics. This support much more recent hardware than the default 4.19 kernel (late 2018 if i remember).

Have an nice day
Lars H

History:
- Installed Beowulf  alone (I use only Linux since 10 years) and from scratch on NVMe. At first reboot I got only black screen with cursor.
- Start the machine with a live system, check 'repository', chroot, make all updates, restart... same as above.
- Chroot it again enable 'backports', install 'firmware-amd-graphics', 'dpkg', update, upgrade, restart... nothing changes.
- 'startx' or 'startkde' don't help either.
- I can use the 'black screen' as 'konsole/terminal' to make update and all other things possible on normal terminal but can't start the UI.

I want definitely leave Kubuntu, Neon is too unstable, Xfce is not for us (200% scaling + flickering to reduce to 150%), MX-Linux is Xfce with sysvinit additionally can be installed kde but scale remain to 200%.

Making experiments with different OSs in the VB see amdgpu-pro drivers all OS recognize the right resolution, Beowulf don't.

Reading file:///var/log/Xorg.0.log  of all machine (real & virtual) something going wrong and need help.

Could someone tell me what and in which order I have to install in order to get the full 3840x2160 resolution?