Exporting MP4

AFAIK the primary difference between mp4 and m4v is that the latter can contain DRM copy protection. So I guess for cross-platform use it might be best to output m4v from FCP's Apple Devices preset and change the suffix to mp4 (did FCP's Computer preset default to mp4 or mov?). So maybe mov differs even more from mp4 than m4v?

The Master Export set to Computer defaults to .mp4.

I’m not clear on whether the OP is trying to preserve HDR. If not the whole process is different and has to be edited, converted using HDR Tools, and color corrected to keep something off the original color and luminance.

“I tried direct export as a Master File but it only saves in as a .mov”

This is not correct. If you change the Video and Audio menu pop to Computer you will get a high quality MPEG-4 file, not .mov nor .m4v.

FCP has various export options but are limited regards fine tuning the output.

Compressor does allow fine tuning, once you setup a Compressor option it can be available within the FCP Share options once added.

Al

You are exporting an H.264 file?

In the finder, change the extension of the exported file from .MOV to .MP4.

MtD

Lower left of the preset browser click + and select MPEG-4 to make a custom preset. Set the video codec to H.264 and the audio to AAC or PCM and use with data rate and audio sample rate you want.

If you want to export from FCP as an mp4 file in H264, export Master File and then in Settings choose Computer instead of Video and Audio.