as I understand them, "[t]he party seeking a preliminary injunctive relief must demonstrate:
1. Irreparable injury in the absence of such an order;
2. That the threatened injury to the moving party outweighs the harm to the opposing party resulting from the order;
3. That the injunction is not adverse to public interest; and
4. That the moving party has a substantial likelihood of success on the merits.
In considering these factors, courts apply a "sliding scale" approach where the more likely a movant will succeed on the merits, the less irreparable harm (to the movant) needs to be shown in granting the injunction."
More at
https://www.law.cornell.edu/wex/injunctive_relief .
Jackson is objecting that the Court is letting the fourth factor outweigh the others, especially 1 & 2.
If people suffer permanent harm as a result of being mis-gendered, e.g., that would be "irreparable" and should weigh fairly heavily against any deficiency in the plaintiffs' "likelihood of success." That said, if a majority of the Court are already convinced that Trump has the legal authority implement the new requirement, then letting factors 1 &/or 2 outweigh factor 4 would simply be to delay an inevitable ruling in Trump's favor.
I'm not a lawyer so this reply should be considered worth what you paid for it.