The research they are talking about is in the British Journal of Sports Medicine.
It's taken apart by here by Prof Alun Willians, Professor of Sport and Exercise Genomics at MMU.
https://www.sciencemediacentre.org/...l-fitness-of-transgender-and-cisgender-women/
"The longitudinal data (pages 8-9 in the paper) don’t show convincing evidence of changes in physical fitness that remove the advantage known to exist between men and women in the absence of hormonal treatment. Indeed, other authors (including me) reviewed essentially the same literature and concluded that performance decreases due to hormonal treatment in transgender women were notably smaller than typical differences between men and women, meaning retention of performance advantage".
Basically, it relies on poor quality studies, including biased self reporting, and comparing trans identifying men who were playing 30% of the sport that the much fitter women comparator group were - and then saying because these trans identifying men had similar attainment to the women this meant they had no advantage. Unfit men on hormones performing the same as very fit women proves exactly the opposite. It proves retained male advantage.