I have an apartment with Fiber to the Home this cable connects to a terminal inside the house, the terminal connects to a device that transforms data from optical to Ethernet usable, then that plugs to LAN 1 (WAN) of the router. I want to setup my deco to takeover the router and do the routing itself and I cant, I tried to get the settings from the router and set the router to bridge mode but that doesnt work as the minute I change from PPOE it fails to go online and telephony doesnt work either. One idea I had is keep the config of the router as is and try to solve the double nat problem and dual dhcp server issue by disabling nat and dhcp on the router, does this fix my issue?

Is it worth making Deco the router over an older and cheaper wifi 6 ISP router and how can I achieve this in a step by step format is what I am looking for here.