TPG will tell you that its not possible to use another router with their service and that you need to run it as a access point through their archer modem/router, this is BS.
Bought the RT-AX88U and called TPG tech who told me i couldn't use my new router. Right. Did some research and followed below instructions and its all working.
https://community.tpg.com.au/t5/Broadband-Internet/ASUS-RT-A…
Im on 100/40, just ran my speed test on a wireless PC about 10 metres away from the router and I got 108/37.
Pretty good outcome. Here is the speed test: https://www.speedtest.net/result/10183923912.png
Ok