[doublepost=1559821285][/doublepost]I am not following on what you mean by "turning off". The messages app doesn't "turn off" as it will remain in docks unless you did NOT put it in the docks. If you simply open it, when you quit, it will disappear from the dock.
If you want to have it remaining in the dock, you have to put it there without launching it. Then when you quit, it will remain in the dock.
Apologies , when I open messages its fine but as soon as i use anything else it closes again , the little dot under it goes off and messages dont come through.