Latest MacOS here, got a machine easily capable of handling this game at high resolutions. I've got my display set to its default which is a *retina* 1920x1080 (so in reality it's actually 3840x2160 with the UI scaled upwards). However, in the Mac client for the game, even in full screen, the maximum resolution I can select is 2048x1152, which renders the game in a way that doesn't really look all that good, even with all the other graphics options maxed out (and I still get decent framerate). In other words, 3840x2160 isn't even an option, though that's the monitor's native resolution.
How can I keep my regular resolution for using my Mac normally, but get ESO into full on 4K rendering mode in full screen?