What is a supporting character?
If you want to do an app for one of these background NPCs, look at the Named NPCs system.
Supporting Characters sit on the cusp between PCs and NPCs. They are characters who are actively played by the person who makes them, but do not have a personal plot or a focus on their own character development. If a character exists only to facilitate the plots of others, then they're a Supporting Character.
If you want your character to have someone important to them (say, a teacher who mentors them), but don't plan to play them... that's fine! You don't need to make them a profile at all. You're capable of simply describing the character and mentioning them to friends without needing to do anything more. You only need to make a Supporting Character profile if you actually plan to roleplay as them.