libx11-dev - 2:1.6.7-1+deb10u2 main

This package provides a client interface to the X Window System, otherwise
known as 'Xlib'. It provides a complete API for the basic functions of the
window system.
.
This package contains the development headers for the library found in
libx11-6. Non-developers likely have little use for this package.
.
More information about X.Org can be found at:

.
This module can be found at
git://anongit.freedesktop.org/git/xorg/lib/libX11