"Not yet supported platform" is displayed on builds we don't support
When a Libretro core isn't present and you try to run a game from the platform it implements, a message states we don't support this platform yet which is true for the Flatpak version, but on other builds the message is very imprecise as instead the users may have to install the missing Libretro core.
Maybe we should use a different message when building for non-bundled systems.