That's an opinion piece. And the 'citations' it gives is a research paper about puberty blockers which is mainly about their use on children with precocious puberty - like 9 year old girls with periods - where the use is short term and limited.
When the paper talks about children with gender issues it actually says
"The impact on BMD (bone mass density) is concerning since lumbar spine Z-scores at age 22 years were found to be lower than those observed prior to treatment [
122, 123],
suggesting a possible permanent decrement in BMD. Thus,
it is unclear how long GnRHa can safely be administered.
The effects of GnRHa on adolescent brain maturation are unclear. GnRHa therapy prevents maturation of primary oocytes and spermatogonia and
may preclude gamete maturation, and currently there are no proven methods to preserve fertility in early pubertal transgender adolescents."
So the article's author's best piece of evidence actually says puberty blockers permanently reduce bone density, might affect cognitive function, and might well leave you sterile.
Can an 11 year old understand all those risks and make an informed decision to consent to all that? Can you decide at 11 that you never want to have children? Childless adult women in their 20's have trouble getting the NHS to sterilise them because they might change their mind. It's crazy to think children can understand and consent to it.