An USB isolator will help eliminate ground loops and cuts down electromagnetic interference (EMI) in between the pc as well as the related unit.1x GND 3V3 (P2 with 2 pins two.54mm) connector can be used to power externally the WCH CH569 MCU (it is usually recommended to remove the P4/SHUNT in that scenario It's not necessary given that the 3V3 LDO