RealVNC Server on Windows Server 2022 without GPU - low resolution

Hello everyone,

I am currently using a dedicated server from Hetzner with an AMD Ryzen 7 processor and Windows Server 2022.

The server has no GPU installed and only the integrated chipset from AMD, which is only recognized in the system manager as a Microsoft basic dispay adapter and is displayed with an error 43.

I have now installed RealVNC server and thanks to this article here: https://help.realvnc.com/hc/en-us/articles/360004012211-Display-issues-when-connecting-to-RealVNC-Server-running-on-Windows

at least a picture is displayed when I set the value to 1 in the registry.

The problem is that I only get a resolution of 640x480.
I can't find any way to adjust this.

I have already tried to change the native resolution of the graphics adapter via the registry, but this is ignored.

Unfortunately, I have not yet found a tool for a virtual screen that runs on this hardware and under windows server 2022.

And the curious thing is:
when I set up the server for the first time, realVNC ran without any problems. 
could it have anything to do with active directory or remote desktop services under windows server?

I would be very happy to receive some hints.
A dummy plug is unfortunately not possible as Hetzner does not offer this option.

Greetings
Sebastian