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. For correct colors, we need !924.
This is a screenshot of XWayland VirtualBox with !924 and !934 and MESA_GL_VERSION_OVERRIDE=2.0 and MESA_GLES_VERSION_OVERRIDE=2.0
Without !924, I will get incorrect colors (#1354), and without !934, I will get black window (#1356).