With Mir focusing on Wayland compatibility now, toolkits and other software making direct use of Mir’s APIs can begin making use of any existing Wayland back-end instead. GTK4 drops the Mir back-end since the same can be achieved with the Wayland compatibility and now SDL is now making a similar move…

Source: Phoronix – SDL Now Disables Mir By Default In Favor Of Wayland Compatibility