Earlier quoted context omitted.
> Why is it an ignorant question? The nicer ones let you use JTAG etc connections, and debug to console using ITM or RTT. (STM, nRF etc) Others allow debugging via serial. Because all those systems, even the very nicest, all over the palnet, very really have "JTAG etc connections," Those are things you attached to the system. You attach them in a complex error prone process, at the end of it you have a different syst…
You connect the debug probe to your MCU (pogo pins or w/e is convenient for the form factor), connect it to a PC over USB, and print to a terminal window in Windows, Linux etc. Or a serial-USB bridge if it doesn't support debug probes. If the MCU is so basic it doesn't support UART, bit-bang it with GPIO. Too easy!
So if you connect up a bunch of wires and everything goes well "too easy" you can get output from some, not all, systems.
What you describe is no what the comment about "print debugging" means, to me.