This statement is true, but I think how it is worded is somewhat misleading. It is not that trans women are forced to join the military, but can serve without being barred because of their gender identity.
According the White House, President Biden signed an Executive Order that set the policy that all Americans who are qualified to serve should be able to serve. He "believes that gender identity should not be a bar to military service, and that America's strength is found in its diversity." The fact sheet further says how it is in the nation's interest for this policy to enact itself because it provides a more inclusive force than what the military is as of now.
President Biden repealed former President Donald Trump's ban on transgender Americans joining the military, according to BBC News. The ban took effect in 2019 and was lifted by Biden in early 2021. Trans personnel who were already within the military were allowed to continue their service, but new recruits were unable to do so.
According to CNN, those who were discharged on the basis of their gender identity will have their cases reexamined. A Human Rights Campaign president, Alphonso David, said that "the greatest military in the world will again value readiness over bias, and qualifications over discrimination."
The ban being lifted appears to be good news for the transgender community, whereas this statement makes it seem like they will be forced to join; however, it is now a choice for them to do so if they want -- it was not a choice beforehand.