Mad props to @camelCaseNick for successfully implementing the first phase of @philippsauberzweig's proposed solution for GNOME Calendar's general layouts and formfactors design overhaul (see https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/1332), a project that has been in the work for many months to solve https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/1007 !
https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/542 has landed in the main branch, you can now try it out in the nightly flatpak version.