Hi @alice alice,
Welcome to Microsoft Q&A!
Do you want to add a C++ Class Diagram to a CMake project?
If so, it is not supported currently. You can see the suggestion ticket in Developer Community:
Class Designer support for CMake based projects - Developer Community (visualstudio.com)
Please vote on that ticket and add your comments there to send feedback. Thanks for your understanding.
Sincerely,
Anna
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