Poor Signal Strength Since Installing V18.3.1

I live in a marginal signal strength area, usually getting 1 or 2 bars on my iPhone 15. However, since installing V18.3.1 software update, I always get the "SOS Only" indicator. My wife's iPhone 8 gets the 1 or 2 signal bars. What's the deal with the software update?

Yes, I have turned the phone off and back on again as well as toggling the "Airplane" mode.

I also used the "hidden" iPhone Field Test feature and got the results shown in the screen capture attached.

I don't want to contact my carrier because my wife's iPhone 8 is on the same carrier and working normally.

What to do?

[Edited by Moderator]