Funnily enough, in Australia we call the broiler a grill, and what you’re describing is exactly what I thought a grilled cheese was. One of my favourite snacks when I was a kid was this, but with corn kernels under the cheese as well. Of course, being Australian, cheese and Vegemite was also a winning combination!
No. This includes 4G and 5G devices. 3G devices will just stop working when the 3G network is shut down and don’t need to be blocked.
My phone is set to LTE only in my modem config, all of my calls are via VoLTE, my phone will still be blocked.