This is and was my very first iPhone. As I decided to give it a try after over 10 years with Android. I have never had such a slow and steady failure like this before. Ever since mid July I would completely lose cellular service for 3 or more hours every week. It then happened every couple of days and the it happened every day, so I had to use my S9 Plus as a backup. No amount of updates would work, iTunes restore and DFU would come back with errors and factory resetting inside ios lead to this. Warranty expired in June and I dont have applecare. I looked up what this image meant and it came up as baseband failure, a hardware issue. I wish you guys well but I don't think I am coming back to iphone anytime soon.
Don’t try dfu or reinstalling the software, this is usually a problem with your particular model and it usually happens when your iPhone antenna is faulty. If you reinstall the software, you might not be able to set up the iPhone. Take it back to apple