This causes people who use Mint-L themes fail to get the theme applied to applications installed by Flatpak out of the box, as found in https://forums.linuxmint.com/viewtopic.php?t=400563
In https://github.com/orgs/flathub/repositories?q=org.gtk.Gtk3theme.Mint we get only the latest Mint-Y themes, and forgotten-to-rename "Mint-Y-darker" themes.
Edit: Mint-X themes are also missing there.