After applying the RT-patch solution - see here, I was trying to install an EtherCAT package without success.
The package is IgH-EtherCAT (EtherLAB), and it works fine on a clear install of JetPack 5.1.1 using SDK manager without RT-patch.
There is an old issue which I was not able to extract any clear actions from it, but it deals with the same problem.
After several attempts, it came down to installing the RT headers.
My question is - how do I build the RT headers and get similar output to the ones extracted from “kernel_headers.tbz2” during “apply_binaries.sh” ?