If there's already a million isekai, why not one more?

After surviving getting transportated into another world, losing his left arm to an ordinary human in the world, surviving a battle royale with 50,000 other people who got transported into the world. He finally got to go home to his home planet but disaster has struck when he was away, dungeons started appearing and other people also received systems like him. Except theirs had more functions, his remained the same. (credits to zhang xu Pinterest for the book cover)