In older releases of Illustrator I could actually open a .cgm file and view/select the line art.
With the newer releases that came out within 2020-2022 I couldn't even open a .cgm (until very recently), even though Adobe said this was one of the supported files in Illustrator. I would immediately receive an error that .cgm was not a supported file type.
This problem has now gone from, I can't open it at all, to I can only open it as a text file. I'm not given a choice, I have to open it this way. This is useless to me. I am at v26.2.1, and I can open a .cgm file without an error, but all I can see is the metadata in text format. There is no line art. This is extremely frustrating and it has been going on for a very long time.
WHEN WILL ADOBE FIX THIS ISSUE?! We all pay good money to use these programs, this should have been fixed long ago.
Perhaps you need to develop a plug-in for this ability??
Draw and design
Import and export
Third party plugins
If you are in control of the CGM export from the originating application, make sure you save your CGM with binary encoding. What you're seeing here is one saved in Clear Text format, and that, to Illustrator is actually seen AS a text file (because that's actually what it is).