No one can match Oskar Eriksson of Sweden when it comes to winning championship titles. In total Oskar has 15 championship wins including that exclusiveWorld championship double of winning both the teams and the mixed doubles titles in the same season, which he did in 2019
Among the women it's the fellow Swede, Anette Norberg with 12 wins that is the most successful. This of course includes the two Olympic golds in 2006 and 2010.
Maybe there shall be an honourable mention to
Bingyu Wang of China that has won 13 international events but two of these has been Olympic Qualification events that are not championships by themselves