Just reading some of the threads here and noticed this one. FWIW, I do NOT use bypass mode, and just have the WAN port of my router connected to the Ethernet adapter. The Starlink router doles out a 192.168.1.xx IP to my router. My existing LAN is on a 192.168.3.XX IP range. Everything works fine.
FWIW, I just connected the WAN port of my existing router to the Starlink ethernet adapter port. Everything on my existing LAN (connected to that router) works fine and i can manage my router's security etc. Of course i can still connect to the Starlink router's wifi, but no real need to.