When I type my name for 5he coffee thing on mobile it just ignores it and gives me the default name
The name was a thing way in the past but since Dave is his own person not a self insert he gets his own name. The coffee cup is now for easter eggs. If you type Dave then you get +1 affection with everyone but if you put someone elses name you get +1 with that person (my fave is how Dave reacts to seeing Tysons name). There's some patreon names that change it i think, but the only one i remember is Timber (i think).