Good afternoon and thank you for posting on the Final Fantasy XIV Technical Support Forums.

What you are describing is an issue that has been reported before. The Square Enix Online Store page mentions issues with Radeon Pro Vega graphics cards. This is likely the issue you are running into.

I can provide some troubleshooting, however, it sounds like your issue is similar to the one already reported:

1) Try adjusting the resolution and graphical settings and see how this affects the glitches.

2) Make sure you Mac is fully updated.

3) Try a clean boot. Restart your Mac, then immediately press and hold the Shift key. The Apple logo will then appear on your display. Release the Shift key when you see the login window.

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!