I text mostly with iphone, still I use messages sometimes on desktop/ laptop.
Usually what delete/ trim off iphone messages, reflect on desktop/ laptop accurately, but no more. And list getting very long and unwieldy.
I brought it up on phone last with a good Apple tech, and we peeked into desktop icloud seem ok right things checked, but never resolved. And laptop has joined the desktop in long list of messages that were deleted from iphone months ago. so gotten worse, thanks!