That was the Sixth Circuit, not SCOTUS
Here's a fuller version of the quote:
The Sixth Circuit reversed. As relevant, the Sixth Circuit held that the United States and plaintiffs were unlikely to succeed on the merits of their equal protection claim. See id., at 479–489. The court first found that SB1 does not classify on the basis of sex because the law “regulate[s] sextransition treatments for all minors, regardless of sex,” by prohibiting all minors from “receiv[ing] puberty blockers or hormones or surgery in order to transition from one sex to another.” Id., at 480. The court next declined to recognize transgender individuals as a suspect class, finding that transgender individuals are neither politically powerless nor a discrete group defined by obvious, immutable, or distinguishing characteristics. Id., at 486–487.
Concurring opinions are opinions of the individual justice(s) who wrote or joined them, not the opinion of the Court.
One of the first things you learn when you study law is the difference between the opinion of the court, concurrences, and dissenting opinions. If you say
"Skirmetti said this", it means that the majority opinion of the Court held this, not that it was in a concurrence.
This article is pretty clear. It's about the courts in Canada but US courts work the same way on this topic.
Concurring or dissenting decisions are not binding; however, they can act as “persuasive” authority that can guide future decisions.
https://www.constitutionalstudies.ca/2020/07/majority-concurring-and-dissenting-decisions/
I'll try to find something on the holding vs the rationale vs dicta/obiter dictum too. Courts may say things in passing that are not binding. It's important to make the distinction between a court's holding and other parts of the opinion;.