I've been running this setup for 3 or 4 months now without issue but the latest updates have broken my ability to use fullscreen.
The only available display resolution is 1024x768.
Prior to the latest update I could use the full screen on my external monitor 1920x1200.
I first saw this issue on the latest 5.2.x version of VBox. Upgraded to VBox 6.0 along with the latest guest additions but still have the problem.
I can go back to my last snapshot (few moths ago using kernel 4.15.0-43 and everything works fine.
Seems like something in the latest updates is causing issues with detecting the monitor resolution.
On the older, working system, when not full screen I can select from many different supported resolutions.
In the latest update these options are all greyed out.
Anyone else seeing this?

Thanks
Tony