Karlsson is coached by Danny Heister at Borussia Dusseldorf and Jorgen Persson for the Swedish national team. He plays left-handed, a trait that adds a unique dimension to his game. His nicknames include "Krille," as reported by hallandsposten.se on 22 December 2016.

Injuries and Challenges

Karlsson has faced several injuries throughout his career. In November 2019, he experienced elbow pain, diagnosed as medial epicondylitis. He underwent surgery in June 2020 and missed two months of training. In 2016, an inflammation in his heel sidelined him for a month between October and November.

Role Models

Karlsson looks up to Swedish table tennis player Jorgen Persson and German player Timo Boll. These athletes have significantly influenced his career and playing style, as mentioned on arla.se on 22 January 2016.

Olympic Ambitions

Karlsson aimed to compete at the 2020 Olympic Games in Tokyo. However, in May 2021, it was announced that his national teammate Anton Kallberg would represent Sweden in the singles event. This decision came despite Karlsson being ahead of Kallberg in the world rankings.

Tokyo Singles Disappointment

The announcement was a major shock for Karlsson. "I was really set on being selected," he said. Despite the disappointment, he acknowledged Kallberg's progress and expressed his determination to not let this affect their friendship or his performance.

Karlsson's journey in table tennis continues to be marked by both achievements and challenges. His resilience and dedication remain evident as he navigates his career with the support of his coaches and role models.