macOS Sonoma caused Final Cut Pro 10.7.1 to struggle with 4K playback?

Hi everyone, it’s my first time posting here! I usually don’t ever write in forums; which I think just shows how desperate I am right now.

A few weeks ago, I finally decided to upgrade to macOS Sonoma on my 2022 M1 Ultra (20-Core CPU, 64-Core GPU, 64GB RAM) Mac Studio after staying on Ventura for a while. After updating, I noticed that Final Cut Pro X has started to struggle with playing back & editing 4K footage. I’ve been using Final Cut Pro X for 7 years now, and have been able to easily edit 4K multicam footage on my Mac Studio. Now, even if I just have a single 4K clip, I get anywhere from 1-5 seconds from hitting spacebar to the clip actually playing.

Things I’ve tried:

• Switching Hard Drives - I’ve tried both Samsung T9 and T7 plugged into the front Thunderbolt ports. Even tried moving all files locally onto the Mac’s own hard drive.

• Uninstalling Google Chrome + Keystone files - Heard that this is a common issue, but it didn’t seem to help me

• Clean / Fresh Install - I’ve completely erased the Mac’s data drive and did a fresh re-install of Sonoma. After only having Final Cut as the single app installed, it still struggled with 4K playback.

• Deleting custom preferences

• Creating a new library & project

• Using proxies instead of original media (I’ve had no problems using original media all this time, so it seemed suspicious to me if I only had to start using proxies now)

I was really hoping that it was just coincidence, and maybe I could troubleshoot it myself. But I’m starting to think that I might just be cursed with combination of macOS Sonoma + Final Cut Pro 10.7.1. I’ve also included my EtreCheck report.

Thank you to anyone who takes the time to reads this!