We just had this very same discussion some months ago.
This other suggestion is asking for an option to lookup chapter information from the old chapterdb (discontinued platform) where no chapters are available in a file. So you might want to look into that suggestion and comment/vote there in order to avoid distracting or cannibalizing votes.
Beyond that… as per Otto’s response:
Chapter editors are available for all kinds of platforms and media formats. It’s fairly easy to do this with MKVToolNix for MKV files. On macOS I’m regularly using “Subler” to edit MP4/M4V files.
