I Am Legend 2 will pick up after the film's alternate ending rather than the theatrical cut. The hit film, which was released in theaters in 2007, starred Will Smith as one of the last human survivors of a plague that turned people into monstrous nocturnal creatures called Darkseekers. While the end of the film originally featured Smith's character sacrificing himself in order to save two more survivors and protect a potential cure for the virus, the alternate ending on the DVD release featured him realizing his experiments on the Darkseekers were causing them pain and forming a bond with the alpha, returning his mate and escaping to freedom.
https://screenrant.com/i-am-legend-2-confirmed-to-make-original-movies-alternate-ending-canon/