For an example of a "real" (positional) queen sacrifice, Rudolf Spielmann presented this game against Jorgen Moeller in Gothenburg 1920.
In the first diagram Black threatens 9...Bg4 winning the queen, since it must not leave the f2-square unguarded under threat of checkmate.
Here Hermann Pilnik (White) is defending an endgame three pawns down, but played Qf2!, when Samuel Reshevsky (Black) had nothing better than ...Qxf2 stalemate.
[4] In The Game of the Century, Bobby Fischer uncorked a queen sacrifice to obtain a winning material advantage.
In the first diagram, White's king is stuck in the center and Black has control of the open e-file.
He can threaten back-rank mate to win even more material; his pieces are coordinated and White's rook is trapped in the corner.
[5] In the World Chess Championship 2016, Magnus Carlsen defeated Sergey Karjakin in the final tie-break game with the queen sacrifice 50.Qh6+!!.