I'm having the same issues, since I updated to 12.3 to use Universal Control. (What's that? Well, it lets you use one mouse across multiple computers, macbooks and tablets).

Anyway, I am up and running now, and here's what I had to do while I wait for SE to fix the launcher that they are charging me extra to use on a mac:

1. As others have said, go to XIV on Mac, do what they tell you to do, if you can't get up and running, use the discord linked on the site. They are very helpful!
2. To help with (not fix) the annoying flickering, turn off Glare and uncheck "Disable rendering of objects when not visible. (Occlusion Culling)". Occlusion culling has been causing Macs issues for a while. For good measure, I also disable Screen Space Ambient Occlusion.
3. Disable sound and only turn it back on once the game is stable for you.

I hope that helps. I've been pulling my hair out ever since I installed 12.3, and this is what has helped me so far. Above and beyond that, that Discord is full of Mac users that know how to get you up and running, too, and like helping you.

Let's hope for a stable fix from SE sooner than later, because 12.3 is going live, like it or not.