I'm finding some issues too on a late 2013 Mac Pro (coffee pot type) running MacOS Big Sur 11.6.4 . I mentioned this in another thread but adding it here.

I run FF14 in windowed mode and on start-up all is fine but frequently after tabbing out of the game to the desktop or another Application, the sound suffers from a crackling oscillating distortion which is incurable till the game is completely restarted.

I tried changing the audio sampling options using the Audio MIDI Setup utility as suggested elsewhere. At the 44.1 kHz default I was getting this distorted crunchy oscillation on the sound. Altering to 96 kHz just intensified the nature of the distortion, when it occurred, to a more intense revving sound.

However, I have found that if I launch the Audio MIDI Setup utility and keep it actively running all the time while playing FF14, then it prevents the problem from occurring even with frequent tabbing out.

I have no idea why that works for me, but at least it is a sort of a workaround for now. I've left the sampling at 2 ch 32-bit Float 96 kHz on my Line Output to speakers.

Maybe that helps someone with a similar version of this issue

System details:
Mac Pro (Late 2013)
3.5 GHz 6-Core Intel Xeon E5
16 GB 1866 MHz DDR3
AMD FirePro D700 6 GB