Hi David, thanks for the reply !
I had try everything ! 4K UHD, 1080P, delete FCPX preferencies . All footage is 4k UHD from a Sony A7sIII.
As soon as I open Final Cut Blackmagic both app preferencies get the wired 720×486 29,97 and I can’t change anything on either applications, when I close FCPX Blackmagic Intensity Pro 4K go to PAL. As I mention above on Davinci Resolve everything works fine and eliminate any hardware/system problems…