It’s about hardware enconding. The problem not only exist in fcpx, and it exist also in adpr and davinci too. If you change to software encoding before render out, it will be correct color or shoot with h264 :)

There’s been a lot of problems with catalina+fcpx 10.4.8. Seems like there might be an AMD driver issue. Might want to try generating optimized media in fcpx for now.

Hello, I have the same problem. My macbook pro 16 and a fujifilm X-T3 hybrid for shooting. MP4 400mb rushes are recognized without bug. As soon as I switch to the H.265 rush the macbook becomes extremely hot and it becomes impossible to use it. My configuration Macbook pro 16, basic model, graphics card 5300 amd 4go. Do you know a way to fix this problem?

I remember this exact thing happening with my Avid from many years ago on ProRes footage. Turned out to be the graphics card. A new driver fixed the issue. Have you looked at the FCP forums and/or Mac forums?

Same problem here... Apple still doesn't fix this issue

yeh,,,definetely Apple is getting better and better without Steve (joking...of course....). That´s the reason because from El Capitan I don´t update until they release new versions.....good luck with that folk...

For some reason I had same problem with 10bit h265 Fuji X-T3 files months before Catalina. Had to make optimized files to do normal editing.

It's not a bug, it's a feature. If you would like to remove this new feature, please send payment of $249. - Apple Customer Care

Send your bug here (they respond) : www.apple.com/feedback/finalcutpro.html