One way to see if it's already installed is to use the System Information application (hold option and choose the Apple menu). Then, under Software in the sidebar, choose Installations. Scroll down the list once it loads and look for Pro Video Formats.
This could possibly solve your issue. You should restart your computer after the installation is complete.
Thanks a lot!! Shutter Encoder helps. When I rewrap to mov without reencoding, I can use the file!! Still its very strange that this file isnt supported natively in final cut. I guess somehow it can be a problem with the old os. Its macOS Catalina 10.15.7 and a Macbook Mid 2012. I should get a new m1 or hopefully m2 mac soon. (hopefully without the touchbar
I contacted Apple Support and (as always) they asked me to reinstall the whole system. Luckily I decided not to format my internal drive and used an external one because I dont seem to be able to install final cut at all anymore. The newest version is not compatible with catalina anymore and I cannot find a way to install an old version. Or is there any option?? This would mean, as soon as I reformat my mac, the system gets unuseable because most apps cannot be installed from the app store anymore. is that right??
Reading through some info, it seems that HEVC (H.265) files first started to be supported in macOS 10.13.
I can confirm this as I have an old 2011 17" MacBook Pro running High Sierra (10.13.6) and it does play back your sample file but without audio in FCP 10.4.6. The re-wrapped file (.mov) does play back with sound. QT Player or the Finder (Quick Look) won't play back the original file but will the re-wrapped file.
I believe the audio "issue" is due to the format being 24-bit ipcm, or, specifically, the way the audio part of the file is formatted. Hence, the files being usable after re-wrapping.
I just used Shutter Encoder to re-wrap your sample file and it changed the audio format to pcm (no longer ipcm) in the new file (using Invisor or MediaInfo to inspect the file). So, it seems that your versions of macOS and FCP aren't yet directly compatible with ipcm 24-bit audio.
P.S. - ipcm (intra PCM) seems to be a more efficient format for recording 24-bit audio, which is likely why it's used by the FX3 and other cameras...