It’s actually possible to use the debugger on the NRF dev kits to flash/debug custom PCBs with NRF chips. So a separate (more expensive) JTAG debugger is in fact not required.
Yes nrf dev boards have an on board j-link, and Nordic provides instructions on how to turn the board into a programmer. Their licensing with segger explicitly allows this as long as you use it for other Nordic devices. Much cheaper than a standalone j-link.
