Do I need to remove my SIM card from my iPhone 10 and put it into my iPhone 12 Pro?

Did you order the phone off of apple or your phone provider if so they more then likely put a new sim in it and all you will need to do is turn the new phone on and connect it to WiFi so everything will set up and activate, you will know it worked when a small pop up comes up on your screen saying “activation Complete” then just make a test call. If this does not work go ahead and toss the old sim in. For some reason if that didn’t work, some network providers do require a imei to be attached to the account and sim for the phone to work you need to go to the store for them to activate it or give your provider a call from another device.