I’d suggest changing the title of your thread to include the word Mac.
The problem is obviously to do with libraries so this will probably attract Mac users to help you.
Windows, KiCad 5.1.12 (but 5.1.10 was the same).
With right-click the menu depends if you click at footprint name or at footprint description. For me it should be the same - just another part of the same position in tree.
Double click opens footprint in editor if click at footprint name or description
@paulvdh’s wild guess is correct. If you ever decide to go back to 5.1.x, select Preferences Menu -> Modern Toolkit (Accelerated).
The fallback option does not work on MacOS, and you just get a grey screen. 5.99/6 removed the fallback option on MacOS, so you only get options that work.