DIAGNOSIS The initial WiFi setup on these can be finicky, especially if your network uses certain security settings (like WPA3) or if you're trying to connect via WPS. The process times out.
FIX Skip the WPS or automatic push-button method. Manually connect using the printer's control panel. Go to Menu > Network > WLAN > Setup Wizard. Let it search for your network, select it, and enter your password using the panel. It's slower, but more reliable for the initial join.
IF THAT DIDN'T WORK If manual entry also fails, your router's security might be the hurdle. Temporarily change your router's WiFi security to WPA2-PSK (AES) only, connect the printer, then switch your router security back. The printer should remember the network.
HEADS UP After you get it connected, if you want to use the Brother mobile printing apps, you'll likely need to also enable 'Brother Network Print' or 'AirPrint' from the printer's web interface, which is a separate step a lot of folks miss.