Discovered that #libadwaita apps can enable the convenience "What's New" button in their About dialog to show release notes: https://gnome.pages.gitlab.gnome.org/libadwaita/doc/main/property.AboutDialog.release-notes.html
Some #GNOME apps already use it: stable releases of Calendar, Shortwave, Showtime, Papers, System Monitor, Decibels, Warp, etc.
I've now filed RFEs for this in Tuba, Epiphany, Contacts, Fractal, Secrets, Warehouse, Maps, Apostrophe, Snapshot, File Roller, etc.
Ideally I'd want to suggest it in Ptyxis, Text Editor, Builder, Loupe & Pika…