On some drivers (mesa included), when we request GBM_FORMAT_XRGB8888, driver set surface storage format to GL_RGB8, which breaks gles2 rendering. If we force set gbm_format to GBM_FORMAT_ARGB8888, then rendering will happen and working.
This is a screenshot of XWayland VirtualBox with !934 and MESA_GL_VERSION_OVERRIDE=2.0
Without !934, I will get black window instead of VirtualBox (#1356).