Hair is the usual culprit.

Yes, at least 90% of the time a frozen side brush means hair wrapped around the axle inside the brush housing. The motor itself rarely burns out first.

Pull the brush off (usually a single screw or snap), then look under the hub. You’ll see a thin metal axle and a gap between the brush and the base. That’s where long hair, thread, or pet fur gets wound tight and stops the brush from spinning. A pair of tweezers or small scissors will pull it out in 30 seconds.

If the brush still won’t spin after cleaning the axle, then check the motor. Spin the brush mounting point with your finger—if it turns freely with resistance, motor is dead. Replacement motors are cheap ($10-$20 on Amazon) and usually just snap or screw into the housing. Worth doing before buying a whole new vacuum.

Don’t bother with “diagnostic modes” or app resets. They’re almost never the fix.