I have updated my reply. No Double NAT for the router behind bridged ONR LAN port.
Singtel TV box --> unbridged ONR LAN port
Last time I was always with Singtel mainly because of stability, but also partially because of the ONT trick --> you can use VLAN capable switch to split the connection into two and get two public IPv4 addresses from Singtel, essentially dual 1Gbps plan but the combined bandwidth is still 1Gbps.
https://forums.hardwarezone.com.sg/threads/working-singtel-vlan-settings-with-tplink-sg108e.5746952/
For Singtel 2Gbps users --> they can also have two public IPv4 addresses from Singtel, after bridging of the SingTel GPON ONR, the bridged port will have no Double NAT, the unbridged ports will still work for interne access and Singtel TV (if Singtel has not changed their backend), essentially become the Singtel 1+1 Gamer bundle plan, without the bundled RT-AX86U router and the WTFast gaming VPN.
There are quite some WC 2.5Gbps plan users who also do the same thing, bridging one port of the GPON ONR. One user even bridges two ONR LAN ports and use Dual WAN Load Balancing to work around the 1Gbps LAN port limitation of the GPON ONR.