Why can't my cellular-enabled Apple Watch Ultra 2 send text messages to any recipient?

Why doesn't my cellular enabled Ultra 2 send text messages? I don't want to use iMessage. Simply RCS, MMS or SMS. The problem only existed previously with recipients who use iMessage, but now after the latest update to 11.4, I cannot send message to anyone. To be clear I could routinely send messages before the latest update to non-iMessage and Adroid users. I can receive message without issue from anyone. If I try to send a message I get a "message failure," and no amount of retries succeeds. Curiously my paired iPhone receives the message, but not the recipient. Not even to my spouse on our own home wifi network. I can send and receive texts on my iPhone without problem. I have the watch settings on my iPhone set to "mirror my phone." My iPhone is at the latest SW update as well 18.4.1. I am using AT&T 5G sim in my iPhone. I can make and receive phone calls, miles away from my iPhone at home on my watch, so apparently the cellular is working just fine. Other apps like NY Times, or airline apps work just fine. I've tried resetting and restarting both devices numerous times. I'm at a loss as to what the issue might be? Will it just not work without iMessage, which I know has issues with Android message recipients...so just that makes it a non-starter.

[Re-Titled by Moderator]