After some investigating it actually looks like a Mac OS issue not a Final Cut Pro issue linked with the 10th gen CPUs so please can everyone also submit a form for Mac OS and report it as a bug report and explain your issue
Here is a sample that I wrote:
There is an issue with MAC OS and the new 10th gen CPUs when using applications such as after effects and Final Cut Pro. There is clearly a bug that is causing this issue. It looks like it's linked to the GPU on these new 10th gen processors potentially with with the G7 graphics. please fix this problem as I'm sure you're aware that many customers are returning these MacBook pro's with these new 10th gen processors because they cannot use it with these Pro apps. I am using Mac OS Catalina 10.15.5
Link is down below:
https://www.apple.com/feedback/macos.html