Hello,
I found a bug when I accidentally closed all viewports. (It can happen fairly easily - I had just closed all but one viewport, and then accidentally right clicked, rerunning the last command and closing the last viewport.)
This put me in a glitched state where the only thing remaining, the default “Page 1” layout was my active viewport, but only showed a black screen. In this state, commands like “NewViewport”, “4View” and everything else I could think of to reopen the closed viewports do not work.
NewFloatingViewport did however work and with a floating viewport open I was able to run NewViewport and get Rhino back into a normal state.
Another way to get back into a normal state is to save and reload the file - Rhino will create a default viewport called “Unnamed”.
I noticed that if you don’t have any layouts you are not allowed to close your last viewport - this should probably apply even when you do have layouts, especially as Rhino creates a layout by default in every new file.