The CompressorKit error is very pesky and has been reported frequently on
this forum of late. It seems to be related to an iTunes update that implants a
64 bit architecture into the system library. Thus, some people have solved this
by upgrading to Catalina, that is a 64 bit operating system. However, that
would render inoperable any legacy 32 bit programs that you may have on your
Mac, and also some legacy media would not play in iMovie and would need to be
converted.
Sometimes booting up in Safe Mode (see Finder menu for instructions) and
immediately shutting down and rebooting in normal mode helps.
Recently there has been a breakthrough on this issue, discovered by
nicocaro, who posted a solution on this forum. Below is a link to the thread
where he describes how to solve the problem by removing a 64bit architecture
from an iTunes update. Other posters have successfully tried the
solution.
Here's the link to nicocaro's solution:
https://discussions.apple.com/thread/251266351
And here as well:
https://discussions.apple.com/thread/251352619
After doing the above your iPhone likely will not sync, although iMovie will
work. To get your iPhone to sync again, see this link that solves that
issue:
https://discussions.apple.com/thread/251916124?answerId=253660165022&login=true
Here's another link, though older, that describes what others have tried
with the Compressor Kit Error:
https://discussions.apple.com/thread/8265338
There may be some proposed solutions in the above link that will work for
you.
I know that your experience with Apple Support was not successfull. However, all
else failing, try calling Apple Support again. The techs there are very savvy
and also have the capability of remotely accessing your computer. Click on the
Contact Support item in the upper right hand corner of this screen and navigate
to a place where you can provide your telephone number so that Apple Support
can call you back. I think that the file path is Contact Support/Mac
OS/Applications/iMovie. Good luck with this.
If you have time, post back with your results, as it may assist others who
have this perplexing issue, and will contribute to our data base.
-- Rich