You can see the pin mapping of the two board definitions here:
- "Adafruit Feather M0 (SAMD21)": https://github.com/adafruit/ArduinoCore-samd/blob/1.7.12/variants/feather_m0/variant.cpp#L25
- "Arduino Zero (Native USB Port)": https://github.com/arduino/ArduinoCore-samd/blob/1.8.13/variants/arduino_zero/variant.cpp#L116
(the Arduino pin number is the index of the g_APinDescription array)
The difference between the two mappings:
| Arduino Pin | Feather M0 | Zero |
|---|---|---|
| 44 | PA6 | PA30 |
| 45 | PA7 | PA31 |
This isn't terribly relevant because there is no "D44"/"D45" on the Robotdyn ATSAMD21G18 development board. PA6 and PA7 are already mapped to Arduino pins 13 and 14 for both board definitions so the pin 44 and 45 mapping on the "Adafruit Feather M0 (SAMD21)" board definition is completely redundant. You could argue that the "Arduino Zero (Native USB Port)" mapping is more useful because it allows you to use the pins SWCLK and SWDIO on the SWD header as Arduino pins.
Let's restrict the discussion here to discussion related to the problem with the boards not producing a port.
Any further discussion of the "Upload Using Programmer" problem should be done on the dedicated topic you created for that subject:
You can post the full verbose output from an "Upload Using Programmer" attempt using your J-Link over on that topic.