Cellular network not working on iPhone 14 Pro Max after iOS 26 upgrade

Since upgrading my iPhone 14 Pro Max to iOS 26, my cellular network stopped working completely. I’m unable to make calls, send SMS, or use cellular data.

To troubleshoot, I downgraded back to iOS 18, and everything started working again — calls, texts, and mobile data were all restored. However, when I upgraded again to iOS 26, the cellular network stopped working once more.

Please, what can I do to resolve this issue?

[Re-Titled by Moderator]

Original Title: Cellular Services not working