Came to say this.

The steam deck is linux. A lot of those launchers check for cheat stuff and os version to make sure you're not cheating. Because it's a windows program running on linux some of the launchers freak out and won't let the game run. Other launchers aren't compatible with Proton (the compatibility layer the steam deck uses) for one reason or another. Like the rockstar launcher for the first few months just couldn't be installed but eventually a workaround was found. If you literally just install windows everything is fine and runs like normal, but not in the native steam os.

This sucks especially hard on Steam deck because it's a piece of proprietary steam hardware and half of all launchers out there don't just work on download. So games like Jedi Fallen Order that were one of the games heavily used in the marketing of the Steam Deck now aren't compatible out of the box anymore due to EA Play.