If you are looking to play Call of Duty: Black Ops 1 or 2, you will need to either purchase a PlayStation 3 or Xbox 360, or you can play the games on a PC.
Yes, you can play Black Ops on the Xbox Series X and Xbox Series S. The Xbox Series X and Series S are backward compatible with a wide range of Xbox One games, including Call of Duty: Black Ops titles. Black Ops is a popular first-person shooter video game series developed by Treyarch and published by Activision.