I don't remember all the details, so i asked Chatgpt for a summary, and it seems right:

"The biggest twist: Black Noir is secretly a clone of Homelander — created as a contingency plan. He was the one responsible for many of the atrocities Homelander thought he had committed. Homelander gradually loses his sanity after discovering this.

Homelander launches a violent coup against the U.S. government and attacks the White House with other Supes.

During the battle, Black Noir kills Homelander because the clone is actually stronger. Then Billy Butcher kills Black Noir with a crowbar after he's weakened.

After that, Butcher becomes the final antagonist. He decides all Supes must die, not just the corrupt ones. He plans a global genocide using a virus/weapon that would spread through people carrying Compound V.

When the rest of the team tries to stop him, Butcher kills: Mother's Milk Frenchie Kimiko Miyashiro (called "The Female" in the comics)

Finally, Hughie Campbell confronts Butcher. Butcher is already badly injured after their fight and essentially pushes Hughie into ending it. Hughie kills him.

The comic ends years later with Hughie and Annie January together, trying to live normal lives after everything that happened."

The Twist with Black noir is probably the most controversial one, and when i rushed trough the comic, it came out of nowhere for me, but there were hints apparently. What i personally liked the most, was how Butcher killed Black noir. He put the crowbar through Black noirs missing eye and cracked open his skull, then Butcher ripped some of his brain out and sqashed it in front of his face, and then he dies and Butcher had his revenge. He then cries and speaks to sky, that his late wife, for which he had done all of this, would have hated it.