Text animation is flickering in Final Cut Pro (Bug)

We have problems with animation text jittering as the animation plays on my partner's iMac (2020). This also ends up in exported video.

We have tried deleting generated clip files, but this doesn't make a difference. We have also just wiped and completely reinstalled this iMac with Big Sur again to fix final cut pro problems, running all updates.

The only way to fix the problem is to delete the text animation clip, and start again, but this is not a solution to fix hours of already edited content that Final Cut Pro is not rendering properly.

We also tried switching playback to high quality but that didn't work. We also have seen GPU rendering issues where the playback might flicker green.

I see this person had a similar issue, but we have not found any solution that works (https://discussions.apple.com/thread/8054794)