The Witcher series is probably the closest one

Also, World of Warcraft. Sure, it’s an MMO, not a regular RPG, but you can complete it entirely on your own, and you’ll get a rich and vibrant world full of enough stories to keep you there for thousands of hours. In fact, I would advise you to start with the Classic version - a remake of 2004 World of Warcraft - so as not to get overwhelmed with content, before heading into newer ones.

Also, if you truly insist on solo/coop play, things like AzerothCore allow you to host a private World of Warcraft server for yourself and/or friends.