The current most popular theory is that the villain Mephisto owns Avengers Tower. That's because The Cosmic Circus reported back in May that Stark sold the tower to Mephisto, and that this would be revealed in the upcoming "Ironheart" series on Disney+.
If you're not a comics person, you're probably not familiar with Mephisto. He has yet to appear in the MCU, though the late Peter Fonda played a version of the character in 2007's "Ghost Rider." Mephisto is the ultimate bad guy in Marvel Comics and even goes by the Devil at times. He has demonic powers, can use magic, and can manipulate time, memories, and reality. He's also almost impossible to injure.
Rumors have claimed Mephisto will appear in "Ironheart" as a tech mogul. But we'll have to wait and see.
