I found this plugin that might be the easiest way to change the Steam Deck boot videos and even allows you to randomize them. So naturally, I wrote a guide for overkill!
How to reinstall Steam OS on Steam Deck?
Successfully setup dual boot Steam OS and Windows 10 pro. : r/SteamDeck
Steam Deck: How To Change The Boot Intro Videos
GitHub - ryanrudolfoba/SteamDeck-rEFInd-dualboot: This repository contains the instructions and scripts on how to install rEFInd.
How to Dual Boot Steam Deck - SteamOS & Windows - YouTube
Accessing the BIOS on your Steam Deck - Pi My Life Up
Custom Boot Animations For The Steam Deck Are Here! Add A Boot Video Your Hand Held - YouTube
The easiest way to change your Steam Deck boot video
Steam Deck | Setting up Dual Boot with Windows and SteamOS! - YouTube
Steam OS missing in boot menu after update. Help? : r/WindowsOnDeck
How to Change the Default Boot Animation on Your Steam Deck - YouTube
How to Dual-Boot Windows on the Steam Deck - Pi My Life Up
How to install Windows on Steam Deck: Dual boot & more - Dexerto
How to get new Steam Deck startup movies - Dexerto