@Blakeproud are you saying your manually forwarding ports?

How do you know your using the right ports?

Have you manually forwarded ports before and had it working properly?

You mention public IP, does that mean your ISP uses CG-NAT?

  @raven-au 

Thanks for the reply.

I have forwarded all the relevant PlayStation 5 ports manually yes.

My ISP was a dynamic IP with CGNAT yet, that's why I made the request to a public IP but to no success.

I have tried turning off and switching UPNP back on​

Power cycled NBN modem, EX75s and  playstaion.

Still showing as NAT 3

  @Blakeproud if I was you I would start from the beginning and verify each bit is working.

Getting a fixed or static IP should allow you to forward ports but IMO manually forwarding the ports is not the best idea.

Not only that you need to use only one or the other.

If you leave UPnP enabled and manually forward the ports it usually will not work, the methods conflict with one another.

So first make sure your internet connection is getting assigned the static address you ISP has assigned to you using the Deco app.

That should be all you need to do to get NAT 2 because UPnP is enabled by default on the Deco.

You might need to be a bit patient and possibly reboot the Deco but it should work.

It will be a problem using more than one ps because the NAT on most routers is symetric only, fullcone NAT is rarely provided on routers.  

In reality all that the router can do for you is forward the ports and it's automatic if you use UPnP and I know UPnP works fine on the XE75.