Constant x86 CPU CATERR detected panic crashes from iMovie.

I can't tell what is happening there. Crashes can happen for a number of reasons. Apparently there is a conflict somewhere. Try the diagnostic procedures below and see if one of those solve it. If not, try contacting Apple Support and talking to the savvy techs there. Unlike here, they have the capability of remotely accessing your computer. You can contact Apple Support by clicking on the Contact Support item in the upper right of this forum's screen, and navigating to a place where you can insert your telephone number.

Here are the diagnostic procedures that I mentioned above:

Safe Mode

You could try booting up in Safe Mode (see Finder menu for instructions) and, after everything loads, immediately shut down and reboot in normal mode. Then see if iMovie works properly.

Resetting the System Management Controller

Try resetting the System Management Controller:

https://support.apple.com/en-us/HT201295

Resetting the NVRAM or PRAM

Try resetting the NVRAM or PRAM, although this issue would be fairly rare:

https://support.apple.com/en-us/HT204063

-- Rich