A useful distinction
A restart button can reset a board while leaving settings intact. It might also discard an unfinished session. Without a clear definition, different parts of the game can retain conflicting values after the player tries again.
Put it into practice
List board position, score, timer, settings and any saved progress. Mark which values return to their starting state. Test restart from active play, a paused screen and an ending. Tell the player when an action will discard information they may expect to keep.