/usr/include/ is in nx-x11proto-core-dev 2:3.5.99.16-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/x86_64-linux-gnu/
/usr/include/x86_64-linux-gnu/nx-X11/
/usr/include/x86_64-linux-gnu/nx-X11/DECkeysym.h
/usr/include/x86_64-linux-gnu/nx-X11/HPkeysym.h
/usr/include/x86_64-linux-gnu/nx-X11/Sunkeysym.h
/usr/include/x86_64-linux-gnu/nx-X11/X.h
/usr/include/x86_64-linux-gnu/nx-X11/XF86keysym.h
/usr/include/x86_64-linux-gnu/nx-X11/XWDFile.h
/usr/include/x86_64-linux-gnu/nx-X11/Xalloca.h
/usr/include/x86_64-linux-gnu/nx-X11/Xarch.h
/usr/include/x86_64-linux-gnu/nx-X11/Xatom.h
/usr/include/x86_64-linux-gnu/nx-X11/Xdefs.h
/usr/include/x86_64-linux-gnu/nx-X11/Xfuncproto.h
/usr/include/x86_64-linux-gnu/nx-X11/Xfuncs.h
/usr/include/x86_64-linux-gnu/nx-X11/Xmd.h
/usr/include/x86_64-linux-gnu/nx-X11/Xos.h
/usr/include/x86_64-linux-gnu/nx-X11/Xos_r.h
/usr/include/x86_64-linux-gnu/nx-X11/Xosdefs.h
/usr/include/x86_64-linux-gnu/nx-X11/Xpoll.h
/usr/include/x86_64-linux-gnu/nx-X11/Xproto.h
/usr/include/x86_64-linux-gnu/nx-X11/Xprotostr.h
/usr/include/x86_64-linux-gnu/nx-X11/Xthreads.h
/usr/include/x86_64-linux-gnu/nx-X11/keysym.h
/usr/include/x86_64-linux-gnu/nx-X11/keysymdef.h