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.
Have you dropped it or was it hit hard or something? Seems like a hardware failure