When launching in windowed mode, switching to (and from) full screen with control-return still works.
This really has me completely and utterly stumped. I have been able to reproduce the behavior on my 5k iMac (2019 Core i9), another 5k iMac (2015 Core i5), and my old 2013 iMac with 2560x1440 resolution.
It occurs in fresh installs of Mojave, and a fresh install of Catalina Beta 8. (i.e. I have not done any non-standard stuff to these systems)
I also ruled out my specific configurations of SheepShaver as the source of the problem by downloading and configuring the September 2019 build from scratch, including fresh preferences, disk images, ROM files etc.
I have also been able to reproduce the problem when using emendelson's SheepShaver wrappers.
Scaling settings have no impact on this issue, nor does any other setting as far as I can tell.
All I can say for certain, is that this problem never occurred before Mojave 10.14.5 or higher.
In High Sierra the problem does not occur.
Once last thing - to make it even harder to trouble shoot, sometimes SheepShaver *will* start up normally in full screen mode. But then I might close it, come back half an hour later and it will revert to the black screen problem. I also see the problem occurring immediately after a cold boot.
I am out of ideas for now.
