If chapter markers exist in a file it would be nice if Avidemux showed them. Perhaps similarly to the way VLC does it.
Long term perhaps they could even be added/removed or dragged around visually.
Avidemux doesn't currently support chapters.
The closest thing would be segments, displayed on the timeline from v2.7.9 (210611).
Support for chapters throughout demuxers, the editor, filters and muxers would be nice to have, indeed. Absolutely not to be confused with cut marks at the border between two segments which mark time discontinuities in the video.