Don't !!! add the brother QL-500 with the default UI of your Ubuntu Linux 18.04 !!!
Use https://localhost:631/
Really! Do this!
You absolutely don't have to install the cupswrapper or lpr drivers from support.brother.com. Just use the usually preinstalled and recommended foomatic driver on your Ubuntu 18.04.
Remove any other instance of this printer in your configuration and use only the one installed by this.