KDE Connect is up high on my list of my favourite open source apps, because it makes transferring files between devices (PC / Steam Deck / Mobile) and more real easy.
There's been a few efforts to get Half-Life: Alyx playable without VR and the latest is HLA-NoVR, out now and it's now possible to play it through, even on Steam Deck too.
ProtonUp-Qt gives you a hassle-free way to install various compatibility tools like GE-Proton, Wine-GE, Luxtorpeda and others for Steam, Lutris and the Heroic Games Launcher.
Open Hexagon is very much Super Hexagon hyped up to max, open source and just absolutely nuts to play. A fresh upgrade is out now and it sounds great, especially for Linux desktop and Steam Deck players.
ROCKFISH Games have now launched EVERSPACE 2 and it looks awesome! One of their original Kickstarter promises did not make it though, with Native Linux support being cancelled as they will support it with Proton instead.
It's official, Valve put The Last of Us Part 1 through Deck Verified and gave it an Unsupported status on Steam Deck. Not really a good look for either Valve or Naughty Dog.
Have a PC hooked up to your TV or need a Linux distribution that might work better on a handheld PC? A new release of ChimeraOS is here, and it's a necessary upgrade. Think of it a bit like SteamOS with fancy extras.