Unlike EmuDeck that has you install multiple things in a list, and have them all separated, the idea of RetroDECK is more to bring a "one-click experience, and to separate retrogames from steam library" the developer says. It comes as a Flatpak to install, and from there it should have everything bundled together. Inspired by the likes of 351ELEC (what it's forked from), EmuELEC, CoreELEC, Lakka, and Batocera.
Powered by EmulationStation Desktop Edition, RetroArch and various standalone emulators it allows you to import your favourites into a tidy environment without flooding your Steam library. Available as a Flatpak you can easily download and install from GitHub, it's still early days yet but the idea is promising enough.
Right now, I couldn't personally get it to work properly and the developer said pretty clearly the current releases are intended for testing so it's one to keep an eye on perhaps. I love the idea of it having things properly integrated, far less hoops to jump through.