GTA V already runs on the steam deck. Even the enhanced edition does https://www.youtube.com/watch?v=QtKjHSn9a5U

Your comment surprised me given GTA V can run on Intel HD 4000 at 40fps with tweaked settings https://www.youtube.com/watch?v=fo2qGdXnabk Which is not so surprising given GTA V is over a decade old at this point.