I have an M1 Max, M1 Ultra, M2 Pro, M4 Pro but not an M5. Your issue could be something unique about your machine, such as a third-party plugin or some nuance of the M5 itself. As Terry mentioned, it could be other conflicting software. That's why he asked for the etrecheck report.
Unlike a non-RAW codec, a RAW video file from a given camera model is unique. That's why I've asked others with R3D-NE material to upload test clips, but no one has responded yet. I've tested a few R3D-NE clips from the Nikon site, but that is not a comprehensive test.
If you can upload some short clips that demonstrate the problem, I'll test those on the machines I have. Use the below link.
If you can upload some of your FCP crash logs, I'll examine those. You can find those by running the MacOS Console app, selecting Crash Reports in the left sidebar, right-clicking on an FCP crash report, and picking "Reveal in Finder." It will have an .ips file extension. Send several of those to me at the below URL.
If at all possible, post the etrecheck report here on this thread. Use the "Additional Text" icon on the forum toolbar. Use only plain text, not RTF, DOC or anything else.
We don't work for Apple; we are just end users like yourself. However, some of us have lots of experience troubleshooting apps in the macOS environment.
https://we.tl/r-3b29S8Lzzl