Earlier today I was able to view my server tree. I clicked something I supposed before I closed the application. I thought that maybe something else happened so I cleaned my Mac Mini Server. I still had the problem along with none of the dropdown windows displaying any entries. When I click the elephant at the top left a window opens with no text and two buttons for Ok and Cancel.
I found this link Messed up pgAdmin 4 menu bar where the person had a similar problem running Windows. I used the information on this link and attempted to do the equivalent actions on my Mac. I moved the ~/Library/Application Support/pgAdmin folder then the application (v 4.1.5) to the trash and emptied the trash. I still have the problem. I also tried to go to my backups from last night to restore the application and the ~/Library/Application Support/pgAdmin folder. I still have the problem.
With all of my searching all I could find about the menu bar is the link above and the documentation link on the pgAdmin about the menu bar. Nothing about how to solve this problem. I could not find any plist related to pgAdmin. I don't know where to go.
Try deleting following directory and restart pgAdmin4 again.
~/.pgadmin