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Open a terminal and run the command echo $XDG_SESSION_TYPE.
If the output is "x11", then your system is using X11.
If the output is "wayland", then your system is using Wayland.
Most modern systems make use of wayland.
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Wayland:
A newer, more secure, and potentially more performant display protocol, especially for modern graphics hardware.
X11:
The traditional display server protocol used by many Linux systems, including Ubuntu.
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