I’ve experienced these “run flat” when I was in an automotive shop. Although you can run them flat briefly if something happens, they may not be repairable when you stop. And they are PRICEY & heavy. Generally don’t get a spare if cars are equipped with run flats. I personally would hesitate to recommend them.
I remember the old Goodyear Double Eagles, they weighed a ton or more.
There are a few different types currently.
https://www.edmunds.com/driving-tips/run-flat-tires-a-primer.html