Quick video explaining how to fix the known issue of the menu bar / top ribbon disappearing / missing in Autodesk Sketchbook. Procedure demonstrated on MacOS Catalina with Sketchbook Ver. 8.7.

Fundamentally it seems like the program tries to enter fullscreen for some reason, and won't allow the user to access any of the controls. Process is demonstrated here for how to fix it. It must be done every time the app opens, but at least it's functional again.