A printer being detected does not mean that it’s ready for use, especially if it requires the installation of drivers. HP printers for example, require us to use the hplib tools to install the necessary drivers.
Please search the forum for “brother”. There are others who have run into this issue and supplied fixes. For example:
I had a Brother MFC-5460CN running as my local network printer/scanner for nearly 15 years, until it finally died. They were ahead of the curve, in 2006. Not so much anymore, but still OK machines.
If you haven’t installed the separate Brother SANE drivers for network scanning, you’ll want those RPMs as well. gscan2pdf is probably the best option for testing the scanner connectivity/communication.
I wouldn’t bother with the silly Scan Key utility, personally. You have to punch a hole in the Fedora firewall for it to be able to listen for commands from the printer, and it’s hardly worth it just to be able to initiate a scan at the printer control panel.
90% of the FAQ / Knowledge Base entries for most models are people having issues with that utility. Not worth it. It’s more convenient and flexible from the Fedora system’s scanning software GUI, anyway.