Chapter Marker Icon in Final Cut Pro 10.4.8 is not active and not be clicked

I'm trying to create a DVD from a long video. I'd like to add ordinary chapter markers.

I have a new download of FCPX 10.4.8 running on Catalina (10.15.4).

I can create the markers just fine but when I click on them to edit them, I can not click on the "chapter icon" at the top of the window. It is inactive and can not be clicked. I can create the other 2 types of markers (blue and red).

I'd appreciate any advice on why this is happening.

Thanks so much.