Since Present is prefered now, in these blocks old order remains: https://git.xfce.org/xfce/xfwm4/tree/src/compositor.c#n2164 https://git.xfce.org/xfce/xfwm4/tree/src/compositor.c#n4342
Olivier Fourdan referenced this bugreport in commit 5ee90cf17c156fd65a79801ceecafb2b2282dea1 compositor: check XPresent before GLX https://git.xfce.org/xfce/xfwm4/commit?id=5ee90cf17c156fd65a79801ceecafb2b2282dea1
Closing.