Trump now able to fire Special Counsel Hampton Dellinger.

This was a decision from a DC appeals court. The DC appeals court is not exactly Trump friendly, but in this case it appeared the make up was fairly neutral (Judges were nominated by Bush Sr, Obama, and Trump). Either way the ruling did not appear to have a dissent, even from the Obama appointed judge. So it would seem like their legal logic is likely not something that the Supreme Court is likely to overrule.
There is some speculation that Dellinger may not want to appeal and allow the USSC to set a precedent regarding this sort of case. Either way Dellinger would only be prolonging the inevitable by appealing. Even if he were to somehow win, the Administration would simply find a way to fire him for cause. They could simply give him a directive that he would likely refuse to follow, and then fire him for insubordination. This is not about a Special Counsel being immune from being fired, but rather it was about the nature of how Trump fired him.
At issue is if Dellinger loses this case at the USSC level, then it would undermine all of the other cases involving Trump firing officers of the executive branch. The High Court could provide Trump (and future Presidents) with almost limited authority to do so. All other challenges would basically be moot. Does Dellinger want to risk that for the chance of being rehired until he is inevitably fired for cause? Perhaps. I suspect someone will at some point, but it only risks providing Trump with more power.
Matt Orfalea on X: "The media response to this year’s State of the Union was different 🤔" / X
Fake News still has a choir
Nevermind
Government ethics watchdog fired by Trump drops lawsuit challenging dismissal