Deleting all messages in a convo on iOS as on macOS?

For a while now, not beginning with iOS15, the option at the top left of the convo to delete all messages on iOS has disappeared. You need to manually select all of them, then hit the bin icon at the bottom.

Whereas on Mac it's the same in the convo, but you can still use the Clear Transcript option in the menu to delete all messages in the convo at once.

Now if you do this from Mac then iCloud syncs Messages and it automatically happens on iOS as well, so that's cool. But you can't do it from iOS, only from Mac.

I'm just wondering WHY the option has disappeared in the convo to begin with, and if anyone has a workaround to Clear Transcript on iOS.

Please don't reply asking "why would you want to..." and such without a solution, it's a question. :)