This guide is deprecated! Please take a look at the defacto un-official SteamOS project HoloISO.
HoloISO is more straightforward to install and is being actively worked on.
This is an unofficial short guide on running Steam Decks new UI on Manjaro. I am kind of a linux noob, so forgive me if I get a few things wrong in this guide. Also, I have not fully tested everything so there may be some weird issues that I have overlooked.