I am sorry, I wrote the message in a bit of a rush yesterday and upon reading it a second time, I realized I forgot to add an important detail: I am simply trying to run the basic blink example.
The sketch runs fine if I follow the standard approach: first flashing the bootloader, then compiling and uploading the sketch through the Arduino IDE. However, my goal is to upload the sketch via SWD without flashing a bootloader first.
Uploading from the Arduino IDE fails—initially due to an adafruit-nrfutil error, and later due to a J-Link-related issue. So I switched to using the command line: I compile the sketch in the Arduino IDE, export the .hex file, and then flash it using nrfjprog. That part works technically, but after flashing, none of the onboard LEDs blink.
I wasn’t just "randomly messing with pins"—I merely tested the four onboard LEDs as defined in my dev kit's pin mappings. Since none of them responded, I assume the code isn't running at all. And I am wondering why the sketch wouldn't run when flashed via SWD, even though the same sketch works when a bootloader is present?
It is true that, as a beginner, I do lack the "correct terminology". I assume it also took you a while to get acquainted with it.