Iphone 7 Sim Card

If you choose the sim free option it will be unlocked and will work with any sim.

If you choose Verizon as your carrierr it will have a Verizon sim inside, which can be removed and replaced with the one from the iPhone 7, but will also be unlocked. It really does not matter in this case what option you go for.

As mentioned Verizon may need to issue a new sim card to make use of 5G, but this is not a certainty.

The Sim card from the iPhone 7 will work just fine in the iPhone 12 for 2G, 3G 4G and LTE. Buy may or may not work for 5G.

To use 5G you need to get a newer sim from your carrier.

It will fit but it will only work if you have cell service from the same company as the 7.

Open the sim tray on the 12. I'll bet it has a Verizon sim in it.