The Arduino Nano uses a bootloader for handling programming the MCU, which requires the USB to serial bridge to be disconnected from anything that could interfere with the programming.

That's because the Arduino Nano 3.0 is intended for breadboarding, where the compact dimensions will leave more space for other components.

Arduino Maker Nano RP2040 “Slightly shorter than a Pico, this board has 30 pre-soldered pins, all helpfully labelled on the silkscreen.