Thanks for the reply but none of it is particularly helpful. (And, no, I’m not using an Apple Watch.). My newest available iOS is 15.7 and it’s installed.
After the first text in a text conversation, my iPhone 11 does not play a SOUND for subsequent messages from the same sender. So if I reply to a text, and the sender replies to me, there is no audible notification. And so on until sometime later.
I’m not looking for groups or summaries or anything elaborate. I simply want every incoming text to play a sound, no matter if my phone already played a sound for same sender just minutes before.