You can do this pretty easily with the Shortcuts app built in to iOS. I have a flow to text my friend whenever I'm near their house.

The Swiss train up already does this. It also tells you exactly where to go with a plan of the station, how full it is where in the train, where the wagon for food is and tons of other things.

CityMapper notifies you a stop or 2 before yours.

There’s a few. I use one called Transit