At the end of Avengers: Endgame, Captain America uses the quantum machine to place all the Infinity Stones somewhere and he returns as an older man.
What happens to the Stones?
The stones are back to their original places and time.
However, he returns as an older one, because he decides to go back to 1950 and live with Peggy Carter, his long-lost love. Steve you see in the end is an old Steve who has lived his life with her.
That dance is part of why the ending of Endgame is such a tearjerker. After Thanos is defeated and the vanished are brought back to life, Steve steps back in the Quantum Realm time machine to take the Infinity Stones into the past and put them back, closing the time loops. But instead of returning to the present, he travels further into the past, where he presumably marries Peggy. The film closes with a flashback of them dancing together in their living room.