A unit reaches Studio over USB-C, Wi-Fi or Bluetooth.
USB-C is the connection to use for firmware work. It stays up while the unit restarts, which the wireless paths cannot promise.
Wi-Fi and Bluetooth suit editing while the unit sits on the board.
When a unit does not appear in Studio, these narrow it down quickly: which of the three connections you used, whether the unit shows the connection on its own screen, and whether a different cable or port changes anything. A USB-C cable that only carries power and not data is a common answer, and it looks identical to one that works.