Tons of RPG games on the system, and you can also investigate some past titles from the 360 and OG Xbox that are backwards compatible such as Lost Odyssey or Dragon Age Origins. I heard Final Fantasy 15 is pretty decent overall, it's an open world RPG and the only reason I did not play it is due to time constraints, I've yet to finish Fallout 4, Dragon Age Inquisition and MAss Effect Andromeda as they are very time consuming, I'm spending more time on smaller-type games these days....but these are all RPG games I enjoy and plan to finish them at some point. There are some JRPGs also but I just don't have the time with those, The SEGA games and games like Ys, Valkarie Chronicles, etc....I don't know if I am getting the names right, some of them may not have released yet....but you should do more research about the JRPGs there are several of them as well if that is the kind of stuff you enjoy.
I'm actually playing Vampyr now, a sorts of Vampire RPG where you have to talk a lot to people and be very careful what you do... you cannot just go attack on any random person because then it affects the story and such, like if you decide to feed on a person then you will never get to see their side storyline, that kind of thing. It's not really a full fledged RPG like Witcher, but there are some RPG elements and you have to talk to people and make choices it's more about that than running around and just using your Vampire skills(edit: keeps crashing at one point, I hope they fix that). Good luck with your search there are a lot of RPG games but I'm not very up to date on that genre right now so many games to play it's crazy