Help with Final Cut Pro and Nikon Z8 ProRes RAW Workflow

The MP4 files are just HD proxy sidecar files that are recorded along with the raw files (ProRes Raw and NRAW) and allow playback in the camera. I just delete them. This is covered in the manual in the section on video recording

https://onlinemanual.nikonimglib.com/z8/en/video_file_types_40.html

I am not clear what problem you are having with ProRes Raw and dynamic range. I don't use Premiere Pro so can't compare but I am somewhat sceptical that it is possible to recover clipped highlights in Premiere Pro that can't be recovered in FCP.

In any case, my big tip is to make sure you don't overexpose in camera by clipping highlights as once they are gone they are gone. I use the in-camera waveform monitor and expose so I am not clipping highlights but I use what is essentially ETTR (expose to the right). So I give as much light as I can without clipping highlights. This gives maximum dynamic range, as it reduces shadow noise and preserves detail in the shadows as well as preserving highlight detail. I use the ProRes Raw Settings in the Info Inspector to make initial modifactions to ProRes Raw files (White Balance and exposure) rather than the Color Correction Effects. This is important. I use the NLog tone mode rather than the SDR tone mode, although for raw recording there is little difference in the end result.

Finally, for what it's worth, I have moved mostly from shooting ProRes Raw to NRAW since Nikon made this available for in-camera raw recording, as it is a lot more efficient in terms of file size and it is possible to record 8K60p rather than the 4K30p max for ProRes Raw with the Z8. This gives very high quality when downsized to 4K. However, unfortunately FCP can't handle NRAW so it means doing the initial grade in DaVinci Resolve and exporting as ProRes to finish the edit in FCP which I much prefer to Resolve for editing.

You need to select the file in the browser, go to the Info Inspector and at the bottom you should see a button saying ProRes Raw Settings. This is described in detail in the FCP help. Search ProRes Raw Settings.

For ProRes Raw the conversion is done automatically unless you decide to change it. You can then adjust white balance, ISO and exposure.

There is no indication that NRAW will be supported by FCP. There is a recent Color Finale plugin that claims to enable editing of NRAW in an FCP timeline but I found it really slow when I tested a trial. I deleted it after a short time. Initial grading in Resolve (the free version works) and export as 4K UHD is way way better in my opinion.

I can't download your file as I am on mobile data right now and the file is too big. If you trim it to a few frames in Quicktime Player and resave as a new much smaller file, it will still be raw.

Would it be possible to see a sample clip perhaps through WeTransfer? I don't know the camera at all, but the AVC file might be a proxy.