The fix position is disable?

As the picture shows, I want to fix the navigate bar on the top, but I can not choose the fix position option. Did anyone encounter this situation before?

Hi there, thank for reaching out! I guess the frame you’d like to fix is on a frame with auto-layout. In that case, when you move to a new frame without auto layout, that should work. This help center article is also helpful:

If you have further questions or if I understand wrongly, please feel free to add a comment!