nx-x11proto-xext-dev - 2:3.5.99.19-3+deb10u2 main

NX is a software suite which implements very efficient
compression of the X11 protocol. This increases performance when
using X applications over a network, especially a slow one.
.
This package provides development headers describing the wire protocol
for various extensions, the client-side libraries of which are provided
in the Xext library.