This is absolutely true. The ACLU, HRC, and the NEA created a document called “Schools in Transition” aimed at and distributed to K-12 schools. https://twitter.com/boysvswomen/status/1359854080424869894
It says that female-only sports teams are sexist, boys who identify as girls are inherently “within the wide range” of female athletic ability, and that there are zero safety concerns for mixed-sex contact sports.
It also says “medical treatment” is a personal decision and that “requiring medical treatment [for boys] to participate in [girls’] sports is inappropriate.”
Link to full document: …https://hrc-prod-requests.s3-us-west-2.amazonaws.com/files/assets/resources/Schools-In-Transition.pdf?mtime=20200713142742&focal=none