KVM Workstation Scale not changeable

Hello, I cannot change the “Scale” value under Settings / Display on the workstation. I would like to set it to 1.25 because everything is currently displayed too small for me. When I set the value to 1.25 and click Apply the screen goes black. After a few seconds I have the old screen and it says 1x in the “Scale” field. The changes are not accepted. What can I do?

Can you figure out how to do this with a Debian VM instead? As per:

Note: I am not a maintainer of Whonix KVM.