Copilot isn't in Visio (at least in the subscription my work pays for).
I used Copilot's chat interface instead, and it is unable to generate a diagram in the Visio .vsdx format; it tried, failed, tried to fix it, failed.
Sigh.
It generates a formatted response but cant edit the document. How stupid you have to be to integrate copilot and not allow it to update text in a text editor??!
If anyone knows how to revert to non-AI version of the subscription let me know