Almost any washer and dryer on the market now has an audible signal (some adjustable for pitch and volume) when the cycle is done, but if you need your phone or watch to be pinged then I guess that's a selling point for you.
I always miss the ding (it's in the basement and very quiet), I'd probably do fine if it simply kept beeping every few minutes, I'd eventually hear one. But just one, nah, not nearly enough.
So, I put a magnetic sensor on the door and made a circuit that starts beeping when the door has been closed for an hour.
Simple as that. Door open, machine not in use. Door closed for less than an hour, probably still running. After that, beep until I open the door. No need for anything networked, no subscription, no terms of service, just more beeping.
(Same with the microwave. There's never a reason to leave cooked food in the microwave with the door closed for a long time, so it dings every few minutes until I open the door. My old microwave didn't do this, but my new one does. It's so simple, why can't they all have this?)
It can be quite the convenience to have a alert which follows your current notification preference settings (e.g. if you're sleeping you don't want to hear the dryer just finished but maybe your SO who is awake does) and can be a quite ding or vibration rather than a buzzer loud enough to be heard across the entire house.
That said I'd much rather it be a simple local HomeKit integration instead of cloud only custom app BS.