Final Cut won't play or transcode my mp4 files

Here is a possible way to troubleshoot this:

• Take the file to the other Mac that plays them.
• Verify they play in Quicktime Player on that machine.
• Use the Quicktime Player's built-in feature to trim a very small piece of that clip. This does "no encode" trimming, so the extracted piece will have all the characteristics of the original long clip. If the original clip has color bars on the header or a broadcast logo, a two-second version of that is sufficient. Instructions: Trim a movie or clip in QuickTime Player on Mac - Apple Support
• Take the little 2-sec clip back to your M3 Max and verify it won't play.
• Upload that 2-sec clip to us for analysis. Put it on a file-sharing site we can access.

Use the button at the top of MediaInfo to show the complete report. Would it be possible to upload a clip to a file sharing site like Dropbox or WeTransfer. You can post a link here which will appear in email notifications.

Studying the metadata, it was probably originally shot on a Blackmagic Pocket Cinema Camera

6K G2 or 4K, or an Ursa Mini Pro. It was probably originally recorded in-camera to ProRes 422, not BRAW. Blackmagic cameras prior to the 12k have internal ProRes recording.

The above file metadata indicates interlaced format, but most Blackmagic cameras cannot record interlaced. The only BMD cameras that can actually record interlaced are the Broadcast series. Those could not record interlaced to ProRes, only DNxHD 1080i.

It was then probably transcoded by FCP or Compressor using an interlaced delivery preset.

There have been a few prior bugs where a few codecs would not play properly on certain Apple Silicon Macs. Those were mostly fixed in current versions. It's possible the other Mac (of unstated type) the OP mentions is Intel.

IMO, the best approach is to update the M3 Max MBP to the latest Sequoia version, including updated Pro Video Formats, and try it again.

Convert with Handbreak to a normal H.264. Before I retired from TV this was an issue with Macs often. A lot of stations use encoders that don’t really produce Mac ready files. The interlace should not be there, it should be progressive.

Could you open one of the files in MediaInfo or Invisor and copy and paste the full report into a reply?

Is there Blackmagic software for the streaming encoder installed on the office Mac that allows it to playback the encoded file?

MediaInfo shows references to a Black-Magic camera and to SMTPE ST 2086 which is HDR. Was the footage shot HDR?

If it's Blackmagic RAW it won't play back in macOS without a playback component. There is most likely one on the BM website, though you may have to use a third party plugin.

Well, obviously something's different between the office Mac and yours. If it were me, I'd investigate what's different between the two -- OS version? Additional BM software/drivers/codecs installed? etc. Also, test your drive containing the files with it connected to the office Mac to confirm it can open the files.

Or, as Ben suggests, punt and transcode with Handbrake.

Is this a camera original? What shot it? It’s extremely unusual to be shooting interlaced video with this format.

I noticed that this is supposed to be interlaced, in H264 codec, which I gather is something that is not well supported in mp4 or mov container.

(I wish interlaced would die already, but alas it seems it is going to outlive us all...)

I understand you can't upload an entire show, but If you could upload a short sample exhibiting the problem, that could help identify what the problem might be.