I also am having this same issue. I have an iPhone 8 and Xfinity Mobile is my cell carrier. I went into the Xfinity Store today and they told me it was an iOS issue. I just updated to iOS 14.2 and the issue is still not fixed. ——-Update——- I just called my VPN and found that my cell data was switched off for my VPN app. When I turned that back on, I gained back my cell data connectivity. Problem solved for me. Hope this helps someone else.