Gender * in the German language

How to write a sentence with its gender-correct version it’s a repetitive discussion in German. But it’s not about if a word needs «der, die oder das». It’s about how to write a sentence that includes all genders. Therefore some started to use the * or the : sign. A well-known language learning app recently used in its advertising for the word language expert the expression «Sprachexpert:innen». This made the female term correct, but the male version is definitely wrong. It’s as bad as I would write «Mann:in». For language learners, it makes the whole situation more complicated.