I found it useful to add the Discover store to Steam as a non-Steam game, and this way I can both update and install what is otherwise desktop mode software from game mode.

all this stuff just confuses me.
Desktop mode is bad for emulation because of bad performance, but everything requires desktop mode to install..

you can somehow run discover from game mode but you have to add command lines and edit some sort of programming or coding within the steam deck in order for gaming mode to read that you are launching a desktop mode app in gaming mode .

When I was young, I had the patience, but now a days my mind is too clouded to even try to understand.

So its not possible to use the discover version of retro arch without installing discover to desktop mode than programming it to launch while in gaming mode and than you have to install rom manager in desktop mode and than configure retro arch in desktop mode but than re launch game mode and somehow magically it all works..

/r/SteamDeck Thread