NX "Create geometry" is greyed out in measure command.

"Create geometry" is not active in measure command when the component is made "make work part". Whereas the same works fine if the top assembly is "work part"

Go to Customer defaults - Analysis - Measurement - Legacy - Allow geometry creation during design in context - Switch ON.

This will allow the "create geometry" active when the measurement is done on "make work part" of child components.