3. Enable the Boot Server in netinstall (net booting) and fill in a corresponding client IP (it is not sufficient only to change the PC's IP)

let netinstall first "search" without boot server, and then powering it on

With Windows, despite repeated attempts the router never appeared in the devices available area. (The IP address of the PC was changed per the docs.) It's not clear to me, whether your netinstall was now successful. However, I had the same issues. Unfortunately, I was not able to fix it under Linux...