This is a common transphobic "gotcha". Let's analyse it briefly.
No, being trans is not a disorder.
But being a girl with unwanted testosterone levels, or a boy with unwanted estrogen levels, or an enby with mismatching hormonal environment, are all medically treatable endocrinal problems.
Depathologising transitude is about letting trans folks access medical service on equal terms with their cis counterparts. Both to prevent, and to remedy the harmful sequelae of these endocrinal problems, using means like gynecomastia surgeries or genital reconstruction.
This is partly why the WHO is reclassifying gender incongruence as a disorder of sexual development. Being trans is not a mental disorder, but a significant portion of trans people do experience an endocrine disorder in the alignment of their gonadal hormones.
This is what medical intervention treats. It is no different than addressing PCOS, or prostate cancer, or hypothyroidism, and it needs to be treated the same way by our medical system. If a cis man has testicular cancer, removing them doesn’t even require pre-auth, but I had to get three letters proving I’m sane and then wait four months to get mine removed, when one of them was a fucking tumor!