Would a virtual HDMI plug fix this?
https://www.amazon.com/4K-HDMI-Dummy-Plug-3840x2160/dp/B07FB8GJ1Z
Oh and what are you using for videocard in the VM?
I also seem to have this issue when using "VirtIO-GPU"
I’ve used this for some of our remote editing 4K HDMI Dummy Plug - High Resolution Virtual Monitor Display Emulator, New Generation Headless Display Adapter Supports up to 3840x2160@60Hz, 1080@120Hz DVI EDID Emulator https://www.amazon.com/dp/B07FB8GJ1Z/ref=cm_sw_r_cp_api_fab_J9qGFbENBTNB5
You could try one of those HDMI dummy plugs and dedicate it to that VM.
https://www.amazon.com/Headless-Display-Emulator-Generation-Single/dp/B07FB8GJ1Z/
You need something like this https://www.amazon.com/4K-HDMI-Dummy-Plug-3840x2160/dp/B07FB8GJ1Z
How about a dummy plug?
https://smile.amazon.com/4K-HDMI-Dummy-Plug-3840x2160/dp/B07FB8GJ1Z