Text Message Forwarding option missing

Yes, my phone number appears correctly in iMessage settings on both my iPad and Mac. But the option for Text Message Forwarding is still missing on my iPhone.

I only have one Apple ID. I am signed in with that account on both iCloud and iMessage on all of these devices, and the Apple ID matches everywhere. But when I turn iMessage back on after toggling it off, it says "Messages in iCloud not available as iCloud and iMessage accounts do not match" (see attached screenshot) — but I've double and triple checked it, and I can ensure you it is the same Apple ID in both places across all three devices. (Also I can still enable Messages in iCloud after seeing this dialog)

My guess is that this is the source of the problem, because it stands out so blatantly as an issue. If this is the case, it seems to be a problem on Apple's end — which means I probably won't be able to fix it. So much for "Apple products just work" I guess.

Update: Nothing has changed.

I've been on the phone with Apple Support twice. The first time, I had a very friendly and helpful representative who was great to work with and easy to understand. Very much the experience I've come to expect from Apple Support. The end of that call was a recommendation to restore my phone and try again, and she scheduled a callback. The second call went more like a call to Xfinity (the opposite of good support, if you're fortunate enough to not know) with a representative that didn't understand what I was explaining, didn't fully grasp what the problem I'm having is, and was very difficult to understand. Eventually he said "I suggest you file a report with Apple's software development team" and ended the call. Calls are monitored and recorded, so if Apple actually cares about this claim of great support than he should be concerned for his job.

I am no closer to a solution to this problem than I was when it started, but I have wasted quite a few hours at this point dealing with an issue that should never have occurred. If anyone has any useful information for me, please do share it! At this point, aimless troubleshooting is taking time away from my job and the rest of life. Technology is at its best when it disappears into the background, and just works — that's why I got my first Mac, because Windows definitely does not "just work" or anywhere close to it. But I've seen over the last few years, especially since 2013, that Apple products only "work like magic" until they don't.