Your macOS version is too new. The driver does not support it.
Fix: Check your exact macOS version. The printer only supports macOS v10.10.5, v10.11.x, and v10.12.x. Catalina is v10.15. It is not on the list.
If that didn't work: Visit http://support.brother.com/. Download the latest driver. Sometimes newer drivers add support for newer OS versions not listed in the original manual.
Heads up: If no updated driver exists, the printer is incompatible with your current OS. You need to use a supported computer or consider a different printer model.