Here is an overview of the demo and game, via Dotemu:

    Demo Features

        Two Levels – Blast through the bustling streets of New York City and take the fight to the Helicarrier levels.
        Choose from Nine Heroes – Unleash iconic moves and experiment with epic duos. Swing in as Spider-Man, slash through as Wolverine, smash as She-Hulk, or rain down lightning as Storm. Other playable heroes include Venom, Nova, Phyla-Vell, Rocket Raccoon, and Captain America.
        Local and Online Cooperative Play – Team up with a friend on the couch or assemble from across the globe.
        Steam Deck – Take the MARVEL Cosmic Invasion with you on the go, as this demo is fully playable on Steam Deck.