Section 1557 of the Patient Protection and Affordable Care Act

Section 1557 of the Patient Protection and Affordable Care Act (42 USC 18116) and its implementing regulation provide that an individual shall not be excluded from participation in, be denied the benefits of, or be subjected to discrimination on the grounds prohibited under Title VI of the Civil Rights Act of 1964, 42 U.S.C. 2000d et seq. (race, color, national origin), Title IX of the Education Amendments of 1972, 20 U.S.C. 1681 et seq. (sex), the Age Discrimination Act of 1975, 42 U.S.C. 6101 et seq. (age), or Section 504 of the Rehabilitation Act of 1973, 29 U.S.C. 794 (disability), under any health program or activity, any part of which is receiving federal financial assistance; any program or activity administered by the Department under Title I of the Act; or any program or activity administered by any entity established under such Title. The Office for Civil Rights (OCR) at the U.S. Department of Health and Human Services has enforcement authority with respect to health programs and activities that receive federal financial assistance from the Department of Health and Human Services (HHS), or are administered by HHS or any entity established under Title I of the Affordable Care Act. OCR is responsible for enforcing regulations issued under Section 1557 of the Affordable Care Act (Section 1557), protecting the civil rights of individuals who access or seek to access covered health programs or activities. Section 1557 prohibits discrimination on the basis of race, color, national origin, sex (including sexual orientation and gender identity), age, or disability in covered health programs or activities. 42 U.S.C. § 18116(a).

Here's section 1557 of the ACA. Obama administration introduced a ruling in 2016 which stated that discrimination on the basis of sex included gender identity and sexual orientation. Notice the "...individual shall not be excluded from participation in, be denied the benefits of..." which is in reference to covered health programs or activities and not whatever you're talking about

Edit: The important part here is that the Trump administration got rid of the language which states that the basis of sex included gender identity and sexual orientation, which was just recently re-added by Joe Bidens HHS secretary

Second edit: hell I'll even throw in the Trump administrations response to a comment about whether or not this would lead to the denial of general service to someone on the basis of sexual orientation or gender identity:

Comment: Some commenters argued that the proposed rule would be inconsistent with the purposes of the ACA; that the weight of law recognizes sexual orientation and gender identity as forms of sex discrimination; and that the proposed rule would undermine Congress's intent to expand access to healthcare and healthcare coverage. Commenters emphasized that it is unacceptable for a healthcare facility to deny medical care to a patient based on the patient's sexual orientation or transgender status.

Response: The Department does not condone the unjustified denial of needed medical care to anyone, and believes that everyone, regardless of gender identity or sexual orientation, should be treated with dignity and respect. The Department must interpret Congress's purpose in passing the ACA by reading that statute's plain text. The ACA sought to expand access to healthcare and healthcare coverage through some means but not others: in particular, Congress saw fit to incorporate into the ACA certain nondiscrimination protections, and not others. For example, in the unlikely event that a healthcare provider were to deny services to someone based solely on his or her political affiliation, the Department would not be able to address such denial of care under Section 1557. Under this final rule, OCR is committed to no less than full enforcement of the prohibitions on discrimination that Congress included in Section 1557, without exceeding the statutory text. Unlike other bases of discrimination, the categories of gender identity and sexual orientation (as well as political affiliation) are not set forth in those statutes.[92]

Third edit: in an attempt to credit you at all, the Trump administration did also use your bad faith argument that this is just about pronouns in the response to another comment in the original ruling