Do I need to transfer the sim

Yes, if you are using the same carrier on the new phone that you used for the old phone. If you are using a new carrier, you will need to get a SIM card from them.

You either transfer the SIM card or get a new one.

Use it only if you want to use the same SIM card for making calls and cellular data services.

If you plan on using 5G cell you need a new sim from your carrier.