Your questions are answered in this Apple Support article for macs and this for iOS, IPADOS except there is no way to turn off pinning a message. However, since you have to intentionally pin it in the first place, then don't pin it.

Last edited by joemikeb; 12/21/21 08:05 PM. Reason: add iOS
If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein