I have a fiber connection in my house that's fiber directly connected to the ISP-provided modem, meaning the modem acts as a convertor from fiber to metallic and I can't get rid of it. The modem also acts as a router and I can't switch it to bridge mode, as it offers no such setting.
I also have my own router (ASUS AX6000) connected to the modem (modem is connected to the WAN slot in the router), however, my router treats the modem as a part of the local network. I can access the modem when connected to the router and I can access the router when connected to the modem (admin interfaces). I can also ping other devices within the network when connected to the modem.
The modem is horribly outdated, insecure and the ISP has full remote control over modem. Is there any way I can make the router treat the ISP modem as WAN, meaning my local network will be hidden from the modem and the ISP?
I would be okay with buying other necessary equipment to make my network more secure.