Creating a new variant and updating the linker scripts in itself isn't enough, unless you're just modifying the files of an existing board. It necessary to also create a new entry for your new board in the Arduino IDE.
It's a bit out-of-date, by here's a guide that shows you what it entails: https://forum.arduino.cc/t/adding-custom-zero-based-boards-to-the-arduino-ide/394499.
There's another guide here: https://www.instructables.com/Arduino-IDE-Creating-Custom-Boards/