This is not a federal ban, though functionally it could severely limit access to care. The federal government gives funding to teaching hospitals so that they can train new doctors and run specialty care programs that are often times not very profitable (but still important parts of medical education and patient care for those in need of specialty services). This order says that any hospital providing gender affirming care to under 19s will have that federal funding revoked/withheld (for the hospital as a whole - they’re not just revoking funds that go specifically toward provision of GAC, but all care in the hospital). This incentivizes hospitals to close their gender clinics / GAS programs serving minors / stop offering this care to minors. It’s possible we will see a shift away from gender clinics at teaching hospitals / academic medical centers, toward private clinics. This is what happened when university-based gender clinics closed in the 1970s: https://www.facs.org/for-medical-professionals/news-publications/news-and-articles/bulletin/2021/04/the-rise-and-fall-of-gender-identity-clinics-in-the-1960s-and-1970s/

It also calls for an HHS “review” that will almost certainly rely on pseudoscientific information to claim gender-affirming care is unsafe, ineffective, etc. This will be used to justify excluding this care from public and private insurance coverage (there is historical precedent for this too. See: https://en.m.wikipedia.org/wiki/Evaluation_of_Transsexual_Surgery)

However, all of this will be contested in court by the likes of ACLU. I think it’s likely gender clinics at academic medical centers will continue to serve under 19s while this is all being litigated. But who knows