I have answered this question several times now, so I figured a top level post would be useful.

Symptom: You bought an EA game on Steam and during the first run you appear to get stuck on the install screen and the messages is “Installing EA App (Script)” and it will not finish or go further.

Solution: When you’re stuck on that screen, use the Steam button and go to POWER->Shutdown. In a moment, the EA App installer will actually appear and you can finish. Once it is done, the Deck shuts down. Start it back up and run your game. Profit.

Third party lockers suck … Sigh.

For those interested in a visual guide, I have a very unproduced video here: https://youtu.be/VMxVIwVvzHI