Success! I’ve moved pgAdmin to a static port. For other Mac users, here is what I did.
Open Terminal window and:
cd ~/Library/Preferences
plutil -convert xml1 org.pgadmin.pgadmin4.plist
vi org.pgadmin.pgadmin4.plist
In the text file, add (I think the area to add this is obvious):
<key>FixedPort</key>
<string>TRUE</string>
<key>PortNumber</key>
<integer>60000</integer>
Save and exit file. Back at command line:
plutil -convert binary1 org.pgadmin.pgadmin4.plist
Close the pgAdmin tab and kill the server using Activity Monitor.
Restart (I found that the updated .plist file wasn’t being seen without the Restart).
You can use any text editor where I used vi. The problem I ran into is that the GUI editors wouldn’t let me edit something in the ~/Library folder, and I’m enough of a Mac noob to not know how to get around that. So I used vi to get the job done.
These details might be valuable in the pgAdmin documentation.