Problem rendering Quicktime MOV in Photoshop

Hi everyone. Hopefully somebody can help me out here

I'm trying to render some animated movie titles from photoshop into a Quicktime mov file, using the default Quicktime options in Render Video as I need the transparent background (the titles are white text on a transparent background). It should be about a 3 second clip.

I've done this many times in the past, changing the Alpha Channel to Straight - Unmatted each time - and I have never had any problems. I've always produced high quality video files with transparency.

Suddenly this isn't working, and I've not done anything differently. I'm stumped. When the video renders, I go the the file, double click to play the video and a pop up says "This file contains some media that isn’t compatible with QuickTime Player"

Is anyone able to help?

I'm using Photoshop v23.4.1 +  macOS Monterey 12.3.1

Thanks