Hello,
According to the information about this printer on Brother's website (offsite link), this printer does not officially support newer versions of macOS; it is possible that the scanner may simply not work on your current macOS version.
The only troubleshooting step that I can think to try is to download the driver for the printer (offsite link); this may allow macOS to recognise and use the scanner, but since the drivers are for older macOS version, there's no guarantee that it will even install.
If that fails, I would recommend speaking to Brother's support, as they will know more about their printer than I do.
I hope that this helps,
Emily