In the linked article they say they will be doing it in the male category as well; they are just doing it in the female category first.
If it would take a while to get everyone tested, it makes sense to bring this in for the female category first. Any female who wanted to compete in the male category would be choosing to do so when it is themselves who are put at risk and a disadvantage. Whereas if males compete in the female category, it is their opponents who are put at risk.
https://worldboxing.org/world-boxing-confirms-mandatory-sex-testing-will-apply-in-the-female-category-at-the-inaugural-world-boxing-championships-2025/
"Under the policy, World Boxing will operate two categories as determined by sex: a men’s category and a women’s category. To be eligible for the men’s category, a competitor must be male at birth. To be eligible for the women’s category, a competitor must be female at birth. [...]
World Boxing’s decision to prioritise testing in the female category is based on a recognition that the issues of safety and sporting integrity in relation to eligibility are most pronounced in women’s boxing. Testing will be applied for boxers in the male category at all World Boxing competitions from 1 January 2026."