When you are in full screen mode and check the Wappler version ( help > about) it opens a new fullscreen tab and it’s impossible to exit the full screen or close this tab.
I have pretty much the same machine and version of Catalina and this is a fact.
Fullscreen mode in Wappler will produce this 2nd uncloseable fullscreen HELP/ABOUT view that obscures Wappler Code editor application.
The same actions as described result in an unquittable tab of full screen blackness which goes nowhere.
I had to Quit Wappler completely to get rid of this 2nd full-screen and useless tab.