I am having cellular data issues as well, on my iphone 11 pro max, my daughters 11 pro max, my other two daughters iPhone 11 and iPhone XR. It says we have service shows the 5g etc but will not load anything. If we send iMessage it won’t go through will send as a text. Phone works fine on WiFi, I’ve reset network settings, removed sim put it back in, hard reset, soft reset, turn airplane mode on and off, turned data on and off, I’ve turned the phone off multiple times. The cellular data worked just fine on all our phones until we updated. I even called apple and Att and no fix!