Why doesn't the menu bar of photoshop 2020 display?

If you are running Windows, check to see if you have more than one graphics adapter active, like one for the video card (likely Nvidea or AMD), and one for the motherboard on-board graphics (likely Intel). If so, de-activate the one for the on-board graphics.

Are you saying that the options for the tool bar doesn't show (that is where you are indicating) or that the menu like File>New doesn's show? If the option bar isn't showing, it is because you don't have a file open. If it is the whole interface, did this just happen or did it happen when you installed? If when you installed, I would uninstall and re-install.

Strange, I can not tell you what exactly is hiding menu bar but I can recommend to you to reset preferences. Backup or save any unsaved actions, brushes... before reseting preferences.