I have a host machine: Ubuntu 18.04 laptop and have SDK manager installed. Used this machine to flash xavier as well.
I want to develop application using Qt and openCV on host ubuntu machine and compile the application,
then in production will flash the program together with Jetson OS to Xavier.
We aren’t using Qt for anything Jetson related at D3 but we do cross compile. We have had good success cross compiling using multi-arch. Most of the software we build uses autotools and we package into .debs. When following that pattern cross compilation is almost completely automatic by executing dpkg-buildpackage -aarch arm64. You do need to install the required arm64 development packages on your build machine but even that is remarkably easy.
Qt may be more complex but I do recommend looking into multi-arch.