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I had a quick look at this Netgear Orbi and it doesn't seem to have an ADSL/VDLS port for NBN FTTN.
So yeah you still need to plug in your Orbi to the TPG Provided FTTN Modem
Hi @thomas2429 as @2fly has pointed out, the Netgear Orbi system will plug into the supplied modem no problem,
Either model that TPG supplies for FTTN will have 4 Ethernet ports, HG659 or VR1600v