Star Citizen needs something like what happened to Freelancer if they ever want to release: change of management. It suffered the exact same feature creep and that only ended when Microsoft stepped in and ousted Roberts
I know people have gotten it to run on Steam Decks in the past. Here’s a guide for running it on Linux in general, though I would assume it also applies to the Steam Deck.
Also, controller support is not a thing in Freelancer, so you have to play with KB&M
Though you might be better off asking in the discord server: discord.gg/FdSkbZ8