Both the Arduino Nano and Uno can be powered via their integrated USB connectors. This automatically supplies regulated 5V power to the board, allowing you to use any USB-supported power source ...
The Arduino Nano and Raspberry Pi Pico support different input voltages, so they also use different power sources. However, they can both be powered with a 5V supply via their onboard USB ports.
For those worrying that [Faransky] is relying on the PWM functionality of the Arduino Nano to generate waveforms, have no fear. At the heart of the device is a AD9833 waveform generator ...