By messages do you mean texts? Because i just tried to delete a random text in a thread of texts, and it worked just fine. I’m on a Pixel 9 using the default Google texting app. I long-pressed the text until it turned white, looked for the little trashcan icon, tapped it, and replied, “yes” to the question that warned me that deleting a message can’t be undone.
When I do that, it deletes the whole thread. Then despite the note that it can only be retrieved for 30 days, it’s simply gone and doesn’t seem to be retrievable.
I just tried on my Samsung S24 w Google messages.
I got @puzzlegal’s result, not @susan’s.
FWIW, I did note that the long-press to trigger individual message selection mode seemed real long. It’s a real press-and-hold-and-wait-then-wait-some-more. When I first noticed this subtopic in this thread a couple days ago, I tried long-press and got no response. I’m evidently more impatient that Google expects. @susan might be too.
The “Are you sure?” message is very different too. The whole thread one says “Chat will be deleted after 30 days. You can block this number to stop receiving new messages” The single entry message says “Delete this message? This action cannot be undone.” You can select multiple messages to delete and then the “Are you sure?” says “Delete n messages? This action cannot be undone.”
So IMO it’d be hard to do the wrong deletion unless your habit is to reflexively click the “Yes” choice on every “Are you sure?”. 
what I was referring to is under Samsung, with an existing thread, I could go down the “line” and select the texts I wanted deleted; Google doesn’t allow that
Thanks! Much appreciated.
It sure does. At least on my Samsung. Read my prior post.
You need to put the thread into message selection mode by long-pressing one of the messages you want to delete until it highlights. Then you can scroll up and down the thread tapping & highlighting other messages you also want to delete.
As you’re doing that, at the upper left of the screen there’s a count of selected messages while at upper right there are icons to copy, trash, or (under the hamburger menu) forward the messages you’ve selected. Once you’ve selected all the messages you want to do something to, tap one of the copy, trash, or forward icons to do the deed.
thanks for all your help!