Drum messages
The drum and the toner are separate parts on Brother lasers, and the drum lasts several toner cartridges. Drum End Soon is a heads-up, not a stop. If you've just fitted a new drum and the message is still there, you haven't reset the counter, which is a manual step the printer doesn't do for you. The reset sequence differs between models, so check the one for yours rather than following a video for a different machine.