Frage: There is NO FCP X High Sierra Compatability!
We clean installed a MacPro 2013, an iMac 2015, and a MacBook Pro 2012 to try High Sierra. Final Cut Pro X will be very slow. If you press Play it won´t play, just after a second. Especially slow with 2 Hour long feature Film Timelines (I mean slower than on Sierra) it is a joke of "compatibility".
Who ist Testing this in your Team Apple? Are you opening a AppleStore mini demo Projects to test this? How is it that you write its compatible. Its not!
We downgraded the machines, wich is just possible if you saved your Sierra Installation or some Bootable Sierra Stick. Just stupid. But FCP X works like before now.
Wait before u upgrade guys!!!!!!!!
Final Cut Pro X, macOS High Sierra (10.13.1)