Is the messagebox that is displayed when I downvote a question or answers disabled?
Currently i only get that blue messagebox on meta only
If you mean the message box that says Please consider adding a comment if you think this post can be improved then that box is only shown to lower-reputation users.
Quoting from https://meta.stackexchange.com/a/2373/140890 (Encouraging people to explain downvotes):
It is shown on every downvote until you get to 2k.
You won't see the box when you have more than 2000 points reputation. Stack Exchange assumes you know by then that commenting on a downvote would be appreciated.