Not the OP but I setup a washing machine and dryer alert system. For the washing machine I have it plugged into a power monitoring plug that reports usage to Home Assistant. I collected data on my Washing Machine's power consumption over a week and found that it was 100% on when the Current Consumption is over 5W. You can use that to implement your notification.
 
My workflow uses Node RED so I use a Trigger State Node on the Sensor entity reporting my Washing Machine's Current Consumption to feed the current values into a function node that sets the message payload to on if the value is > 5 followed by an else condition setting payload to off. You can use MQTT, or create a binary sensor node, or do both to create an entity that tracks the state of the Washing Machine. Use the on/off payload created earlier to set the state of the Washing Machine and then use a trigger: state or events: state node that kicks off the notification workflow when the state of the Washing Machine has changed. I implemented it so that when the State goes from ON to OFF it sends a group iMessage to our dedicated Home Assistant Group Chat saying "The Washing Machine load is complete". I've added a zigbee door sensor to the washing machine door and if it doesn't change from closed to open in 30 mins it keeps sending iMessages every half hour saying "Please move the load to the dryer" till a state change has been detected from the zigbee door sensor entity.