Just wanted to give an update here. We currently don't have a fix planned for this as other issues like crashes and FPS issues have taken priority. Right now you can play in either Windowed or Fullscreen mode.
They announced a timeline on performance updates.
It's unacceptable how long it has taken to fix the Mac client. It shouldn't take a year for crucial issues like unexpected crashes to get fixed. I can only assume Mac support, and therefore Mac players, are no longer a priority to ZOS.
I've cancelled my ESO+ subscription over this and will likely stop playing if it doesn't get fixed before MacOS Catalina is released.
Another month, another no-show from the officials....