There were 5 studies presented as evidence. count them.
1: Korte 2008 This talks about Gender Identity Disorder not transgender. the article is an overview of Currently debated topic involving gender identity disorder GID is a catch all category for all issues of gender nonconformity. THE line "Only 2.5% to 20% of all cases of GID in childhood and adolescence are the initial manifestation of irreversible transsexualism." appears only in the introduction and is not supported in any way or even given an explanation of just what irreversible transsexualism actually is.
2 "An analysis of 10 published studies can be seen here." The first of their published studies was from 1972. Lebovitz, P. S. (1972). Feminine behavior in boys: It identifies transgendered individuals as men who occasionally cross dress. Well I'm convinced
3. The most recent study in this group, published in 2013, confirms that gender dysphoria does not persist in most children past puberty. It doesn't show this at all. what the study does say is that children who identify being the opposite gender persist in that identify through adolescence.
4 In this Dutch study they identified 127 children who were referred to the Gender Identity clinic in Amsterdam. the children were referred to the clinic for diagnosis not because they were trans
5. The latest follow-up study of boys experiencing gender dysphoria (Singh, Bradley, Zucker, 2021) shows the same result as the earlier studies
this may have been published in 2021 but relies of data from 1989 when there was an entirely different set of criteria to diagnose gender dysphoria.