Not tested…
$ flatpak config
languages: *unset* (default: fr)
extra-languages: *unset*
$ flatpak install flathub org.gramps_project.Gramps
1. org.freedesktop.Platform.GL.Debug.default 24.08 i flathub < 551,3 MB
2. org.freedesktop.Platform.GL.Debug.default 24.08extra i flathub < 551,3 MB
3. org.freedesktop.Platform.GL.default 24.08 i flathub < 156,8 MB
4. org.freedesktop.Platform.GL.default 24.08extra i flathub < 156,8 MB
5. org.freedesktop.Platform.openh264 2.5.1 i flathub < 971,4 kB
6. org.gnome.Platform.Locale 48 i flathub < 387,1 MB (partial)
7. org.gtk.Gtk3theme.elementary 3.22 i flathub < 1,3 MB
8. org.gnome.Platform 48 i flathub < 399,2 MB
9. org.gramps_project.Gramps stable i flathub < 74,9 MB
Proceed with these changes to the system installation? [Y/n]: n