Floo Around the World Trophy in Hogwarts Legacy

The 83 Floo Flames are the fast-travel points. The map marks every one, though those out in the open world only once you have uncovered the map around them. The ones you have not lit are grey. Most come along with quests. For the rest, set a waypoint on each grey one and walk up to it. PowerPyx's Floo Flame guide has a screenshot of where each one is.