I had a similar issue after the IOS 15.1 software update, I had an XS too. I no longer had any cellular data connection to my device. After hours of back and forth with apple support and my wireless carrier customer service, I was basically told by apple “it wasn’t our fault, updates are supposed to fix problems not cause them.” And my wireless carrier said that there wasn’t anything wrong with my sim card etc. I was forced into buying a new phone. I only had the XS for a little over a year