Monitor connection callback doesnt get called on Ubuntu

Monitor changes on X11 are also polled when events are processed:

If you are able to build GLFW from the Github source with cmake you can run the events.c test to check if this catches your monitor connection/disconnection. If there is a problem with that then this might be a bug. Note that GLFW only supports a single X11 screen (see _glfwPollMonitorsX11 only returns main X screen display(s) · Issue #1927 · glfw/glfw · GitHub and Only one monitor detected X11 - #11 by elmindreda ), so if the monitor is registered to another X11 screen in your config it might not get polled.