Xiaomi Air 4 lite power instructions unclear

Im planning to flash custom firmware on the Xiaomi Smart Air Purifier 4 Lite (zhimi.airp.rmb1). The wiki shows UART connections for flashing, but it’s unclear how the board should be powered:

Should it be powered via the main unit plugged in?

Or is it recommended to supply 3.3 V directly to the PCB?

Could you clarify the recommended method

Thanks!