Have you tried this?
Board Not Detected
Sometimes the board is not detected even when the board is connected to your computer. This can be solved through the following steps:
1. Connect the board to your computer via USB.
2. Place a jumper wire between the REC and GND pins on the board, then press the reset button.
Place a jumper wire between REC and GND pins.
3. This will open the mass storage device. You can now remove the jumper wire.
Source: https://docs.arduino.cc/tutorials/nano-rp2040-connect/rp2040-01-technical-reference/