In Find Friends in iOS, what does a yellow dot with a star in the middle mean?

This means that the friend is selected as a favorite: Locate a friend in Find My on iPhone

"Mark favorite friends

Favorite friends appear at the top of the People list and are marked by a star.

1. In the People list, find the person you want to mark as a favorite.
2. Do one of the following:

• • Tap the name of the person, then tap Add [name] to Favorites.
  • Swipe left across the person’s name, then tap the star.

To remove a friend from your Favorites, swipe left and tap the star, or tap the friend, then tap Remove [name] from Favorites".