How can I know if my brand new iPhone supports dual sim?

As stated all models will have dual SIM capability, either by way of eSIM+Nano SM slot, or dual Nano SIM slots.

The A2341 is for the US market, thus will have an eSIM plus a Nano SIM slot.

If purchased in China, Hong Kong, or Macau, it will have dull SIM slots, all other regions will have one eSIM, and one Nano SIM slot.

The e-sim needs a supporting network to activate it. Some network carriers will issue an activation code via QR or text.

Some may be activated right onboard the phone ( tend to be directed at international roaming carriers and can be expensive )

And many many carriers simply don’t support e-sim period.

In fact support is actually pretty limited.

The Asian specific dual sim phones have far more appeal and support in their requisite markets.

Mainly this is a consequence of the way mobile markets differ round the world.

In the UK and indeed much of Europe the preference via termed contracts with extensive roaming ( at reasonable rates within the EU. The UK looses those next year due to Brexit)

So the deployment of dual sim devices remain very small here.

Hope that’s insightful.