Singtel can't be testing every single router out there in the market and thus unable to officially claim they support.
From my own experience using Singtel Mesh, one main unit has to be connected directly to the ONR, so really no point using own router unless you do not want ONR and want to use own router with ONT.
Any router should work if it's just for internet. But if you require Singtel TV, you'll either have to use singtel's own router, then connect your router to it, OR use routers with VLAN presets (e.g. Asus).
As for Mesh on top of all that...It may require some expertise on configuration, due to VLAN tagging, esp if you are also going for Singtel TV. Router used definitely need to support VLAN tagging. Asus' presets may or may not work (for Mesh); manual config (if router supports) not simple.