If you haven't started porting your apps yet, check out this article by nostr:npub1w4pg5k7jx8cnj2wsdky7x99ldef8mkrtgqef4lpr5ktcp5fkwq0sp33gaa: https://blogs.gnome.org/alicem/2023/06/15/rethinking-adaptivity

There's also a migration guide to the new widgets: https://gnome.pages.gitlab.gnome.org/libadwaita/doc/main/migrating-to-breakpoints.html