Valve added a hidden menu to the Steam Deck that will allow customizations like changing the boot menu.
Valve has added a new, still-hidden customization menu to the settings screen of the Steam Deck in the latest preview build of steamOS.
This menu will allow you to change the startup movie, similar to the previously featured plugin. It also confirms that Valve will be adding startup movies to the points shop — the same place where you can currently get alternative keyboard skins.
First spotted by Stephen Radford, this is the same feature that data miner Pavel Djundik has previously leaked.
Just note: It might still take a while until this feature gets officially pushed to the stable build, as it's still hidden under preview.