It seems there may be a misunderstanding in your statement. Beyoncé Knowles and Jay-Z are not known as professional boxers, and competing for the unified middleweight championship at the MGM Grand Garden Arena is not something they are associated with.

Beyoncé Knowles is a renowned singer, songwriter, and actress, known for her powerful vocals, captivating performances, and influence in the music industry. Jay-Z, on the other hand, is a highly successful rapper, songwriter, and entrepreneur, recognized for his groundbreaking contributions to hip-hop and business ventures.

While both Beyoncé and Jay-Z have performed at the MGM Grand Garden Arena in Las Vegas for their respective concert tours, they have not participated in boxing matches or sports competitions at the venue. Instead, they are celebrated for their achievements in the entertainment world and their influence as cultural icons.

It’s important to rely on accurate information when discussing celebrities and public figures to avoid spreading misinformation or confusion. If you have any other questions or topics you’d like to explore, feel free to ask!