FCP/Compressor issues - Mac Studio M1 Ultra MacOS Ventura

Hi - I'm experiencing significant compression issues using the latest versions of FCP and Compressor on a Mac Studio M1 Ultra running MacOS Ventura - when selecting the category "Youtube and Vimeo up to 4K" (Bitrate 15,000kbps, 1920x1080). The issue remains the same both when exporting directly from FCP and when running Compressor stand alone on the ProRes 422 file. The ProRes 422 source file itself looks fine.

The pixilation is so significant that I cannot deliver jobs to my clients. Have attached screen shots of compressed frame versus ProRes 422 frame

Has anyone experienced a similar issue with Mac Studio M1 Ultra/Ventura? Any suggestions?

NB. When exporting the exact same FCP project using my old 2013 Mac Pro - everything works fine.

System details:
Apple Mac Studio M1 Ultra 64GB MacOS Ventura 13.0
Final Cut Pro 10.6.5 Build Version 405627
Compressor 4.6.3 Build Version 405609

That's definitely strange. I use Compressor (and it's presets through FCP's 'share' function) all the time without issue, using a few dozen presets I configured myself. I'm not running a Studio though, just a lowly M1 Mini...

15+ Mbps should be plenty for 1080 content, I typically use 10 with great results. Have you tried setting up your own preset(s)?

Would it be possible to get a piece of your media that has the problem so we can test it? Perhaps you could send it using Dropbox or WeTransfer and post a link here. 

Maybe try creating a custom preset with similar settings to the built-in preset?