Warning: if haven't seen the latest episode of The Falcon and the Winter Soldier yet, this article contains spoilers so read at your own risk!
Over the last couple of episodes, The Falcon and the Winter Soldier has revolved around the mystery surrounding an individual called the Power Broker. Turns out, that person was the mastermind behind The Flag-Smashers, a group of Anti-Nationalists who believe that the world was a much better place following the blip aka Thanos' snap.
In Episode 3, titled "Power Broker", it was revealed that the mysterious individual who has been running roughshod all over the world was in fact in possession of the new supersoldier serum which gave the Flag-Smashers their superhuman abilities, and in fact, he or she was responsible for funding the recreation of the said serum with the help of Dr. Nagel who was able to complete and replicate the formula 5 years after he returned from the blip.
Nagel also revealed that he was able to formulate 20 vials of the said serum which could still be in the hands of the Power Broker. However, he wasn't able to disclose the true identity of the villain as he was shot dead by Zemo himself. Now, you may be asking, who exactly could be this mysterious Power Broker?
Following Episode 3, there is now an ongoing theory suggesting that the returning Sharon Carter is in fact the Power Broker. It may come as a huge shock to a lot of people but when you put the pieces of the puzzle together, it actually makes sense. It's worth mentioning that Nagel said that he was hired by the CIA to work on the serum and Carter happens to be a former CIA agent before she was terminated following the events of 2016's Civil War where she sided with Team Cap.
It's also quite interesting how Sharon refuses to come back to the United States when Sam offered to help her clear her name. Sure, she's currently an owner of an art gallery in High Town, Madripoor but what if she's actually taking care of "other" business? What's even more intriguing is the fact that following an explosive altercation in Dr. Nagel's base, Sharon would leave Bucky, Sam, and Zemo and met up with a mysterious woman, telling her that they have a "big problem".
I'm guessing she's out for revenge against the U.S. government herself which is why she formed a group of rebels much like herself who would be later known as the Flag-Smashers. Of course, this one remains a baseless theory for now so take it with a grain of salt but it wouldn't be so shocking if Sharon ends get being revealed as the Power Broker.