There is no all-encompassing "actual X11 fullscreen", X11 does not have an API for applications to have control over the entire screen like you'd find in, e.g,

There is no all-encompassing "actual X11 fullscreen", X11 does not have an API for applications to have control over the entire screen like you'd find in, e.g, DirectX 9 (what most people think of with "real fullscreen" in Windows). What games (and SDL1) ages ago did was to use APIs that changed the video mode and APIs that captured input, both of which are completely separate (they're even from different sources: the video mode API is from an extension, the capture API is from the core protocol) - and then created a borderless window the normal way. There are three different aspects here, each one can be done differently and all can be (and have been) mixed or ignored: 1. Set the video mode. You can either do that or not and use whatever the desktop is running at. You may want to change the video mode not just for resolution but for using a different refresh rate. Both native games (like, e.g. Quake source ports using SDL2) and Wine still do that (you can disable the modesetting in Wine via the registry so that games only see the desktop resolution as the only available one). 2. Create a fullscreen window. There are two ways to do that: either create a window that bypasses redirection ("redirection" here means that the window manager wont manage it, it has nothing to do with compositing - if a compositor is used - though some compositors also use it as a hint for that) and have it cover the entire desktop area (you may want to use randr to figure out the monitor area for multiple monitors) or alternatively use the fullscreen hint on the window and let the window manager handle this. Note that some window managers may not support this or have bugs with it. 3. Handle input. X11 provides an API to capture mouse and/or keyboard input, though strictly speaking this is not really required and TBH i do not see why games ever did that (i can only think of conflicts with other programs but i'd expect this to be something for the user to deal with). In any case, it is rare for games to do that these days. You can just handle input "normally" like any other program. You can provide a (by default disabled) option if you really want to though as the API for capturing is trivial. For my last game engine i did #1 (with an option to use whatever the desktop resolution is) and #2 (using the fullscreen flag by default with the redirect flag as an alternative for window managers that had issues with the fullscreen flag) but i didn't bother with #3.