xorg-server-source - 2:21.1.7-3+deb12u7 main

This package provides original Debian (with Debian patches already
applied, and autotools files updated) sources for the X.Org ('Xorg')
X server shipped in a tarball. This enables other projects re-using
X server codebase (e.g. VNC servers) to (re-)use officially
Debian-supported version of the X xserver for their builds.
.
Unless you are building a software product using X server sources,
you probably want xserver-xorg and/or xserver-xorg-core instead.