Many thanks for this working hint.
However: It’s a little bit tricky. Right click and “save to favorites” on a finished title would have been much easier and more Apple like. Unfortunately Apple is currently destroying the ease of use of their software. I still can’t believe it, that chapter markers are missing in FCPX. Also Compressor 4 can not add chapter markers if you export to a H.264 MOV. You must export to a H.264 M4V format, that – manually set in compressor – chapter markers are added to your output. That’s really worst… 🙁