CMX is legacy and read-only here
CMX is an older vector format. It can usually be opened and converted from, but it's long obsolete, so there's no modern encoder to create new CMX files.
Looking for AI to CMX? Here's why CMX isn't an output option — and the modern formats to use.
We don't create CMX files — it's a legacy format that's effectively read-only. Here's what to convert to instead.
CMX is an older vector format. It can usually be opened and converted from, but it's long obsolete, so there's no modern encoder to create new CMX files.
For a file that opens everywhere, convert your AI to SVG, PDF or EPS instead.
AI is Adobe Illustrator’s native vector format for logos, icons and illustrations that scale to any size.
How to open AI files open in Adobe Illustrator and many vector editors.
Full AI format guide