Up to now, PhaseOne has had a pretty strict policy when it came to supporting third-party medium format cameras. It was watered down a bit when they made a deal with Fuji, so the Fuji GFX series is officially supported since version 11.3.
Now three major versions later, PhaseOne added support for the Pentax 645Z in yesterday’s latest update of Capture One 21 (14.4.0).

This decision changed a lot for Pentax 645Z owners who had to tinker with the EXIF data to trick Capture One. As the sensor of the PhaseOne IQ250 and the Pentax 645Z are basically the same, faking the EXIF data was enough to work with the files.
Unfortunately, the colours tended to be way off. A carefully crafted ICC profile was needed to fix this problem mostly.

I will check the quality of the raw conversion and compare it to the fake IQ250 images.
Stay tuned for a follow-up.