You have a couple of choices; in your Clover config.plist, set Inject-ATI to be false and go about your usual computing. This will use the generic AMD Frame buffer and give you full metal support and acceleration. Pretty close to OOB plug and play. Or set Inject-ATI to be true and set a frame buffer name into place along with a patch to allow Clover to use the buffer. (go to this thread:
https://www.tonymacx86.com/threads/...rs-for-new-amd-radeon-drivers.197273/page-251 and search backwards for the patch(es) by Mork. The one for Sierra uses the Berbice frame buffer, you will also get metal support, full acceleration and some cosmetic niceties. -- there is also one for 10.11 much further back in that same thread, if you are still using that.)
Also, possible but you will have to do some checking because it seems to depend on the version of FCPX you are using, as well as the version of Clover, the version of macOS beta, etc., etc.
If you are also considering the RX470 or RX 480, or the newly released RX5nn versions, those cards require some kext editing and Clover patching, but most folks that use them seem to really like them for FCPX editing.