Second installing Heroic or Junk Store. Get those Epic freebies, but games in GoG sales as well.

As you are new with the Deck though, using Heroic does involve using desktop mode. If you have Minecraft, you can set up Prism Launcher as well. There’s also EmuDeck for emulating older systems.

This is a bit more involved than just buying Deck verified games on the Steam store though. Get comfortable with it first. Watch some YouTube tutorials.