When your electric lawnmower is smoking it's usually because the motor is overheating or is burned out.
Or if the electric lawnmower has a belt it could be the belt slipping and causing the smoke.
Worn out electric motor components like brushes can cause excessive heat generation and friction and cause the electric lawnmower motor to smoke
If your electric lawnmower is smoking you should shut it off and unplug it.
Then feel if the motor is hot and if the motor is hot then it's a sign that the motor is burned out and no longer good.
Electric lawnmowers typically last 5 years to 7 years depending on how often they're used and how well maintained they are.
Also mowing through tall grass with the electric lawnmower can also cause the electric motor to work harder and overheat and damage the electric motor.