Currently, when given the choice, Xwayland will pick the GBM backend over the EGLstream backend if both are available, unless the command line option “-eglstream” is specified.
The NVIDIA proprietary driver had no support for GBM until driver series 495, but starting with the driver series 495, both can be used.
But there are other requirements with the rest of the stack, typically Mesa, egl-wayland, libglvnd as documented in the NVIDIA driver.
So if the NVIDIA driver series 495 gets installed, Xwayland will pick the GBM backend even if EGLstream is available and may fail to render properly.
To avoid that issue, prefer EGLstream if EGLstream and all the Wayland interfaces are available, and fallback to GBM automatically unless “-eglstream” was specified.
With this, the compositor, given the choice, can decide which actual backend Xwayland would use by advertising (or not) the Wayland "wl_eglstream_controller" interface.
This change has no impact on compositors which do not have support for EGLstream in the first place.