I've already told you, Arduboy2 is a library, not a board. It will not show up as a board.
The Arduboy2 library is installed using the Arduino IDE's Library Manager:
Sketch > Include Library > Manage Libraries...
Sketches will then automatically use the Arduboy2 library if they require it.
When you use menu
Tools > Board:
you should always select
Arduboy. If you haven't installed board support for the Arduboy and DevKit, you can select
Arduino Leonardo instead. Selecting either
Arduino Leonardo will both work the same.