Capture live video with FCPX at ATEM mini - Yes it is possible.

I CAN capture live video coming out of an Atem Mini using the Import command of Final Cut Pro X.

Record ATEM Live video to FCPx

https://www.youtube.com/watch?v=1OxwKltU2Fc

I just load up the Prezi Video app and capture the video from the BlackMagic.

Open up Final Cut Pro X and select Import and your signal is there.

I use this all the time to record fresh Smart Film School tutorials "live to tape" in one take. Then I can clean up and add animation overlays in FCPx - A super-fast workflow with no transfer time or ingesting of recorded media.

Prezi does mess with the system video subsytems of OSX "at the metal" and will make your BlackMagic camera not appear in video chat apps like Zoom.

So, I find that I have to run the SUDO command at the terminal to reboot the Core Video VDCA Assistant after a recording session.

Open terminal and enter this command.

sudo Killall VDCAssistant 

And I have to hard reboot my Atem Mini. (unplug power, wait one minute, plug back in)

So those are the workarounds until Apple can understand that the BlackMagic Atem Mini is a valid Web Cam source and they support it.