Not every unjust, stupid, or evil thing is illegal.
Even when something is illegal, that doesn't mean you have standing to challenge it in court, or that a given court has jurisdiction to do anything about it.
Courts (theoretically) follow rules. They can't just randomly set things aside without some basis in those rules. Lawsuits are not a magic universal remedy.
You could definitely argue that courts don't always follow rules, and that the Trump administration is doing everything it can to make that worse, but the changes they're making aren't going to work in your favor, because those changes are in the nature of "we can do whatever we want, and fuck the courts if they don't like it".
The true american dream.
What they did not do was to sue their way into power. I mean, yes, they used the courts at a few key points, but that wasn't the core of it, and the smart money says they could have done it without, say, Bush v. Gore.
The new court approaches of the 1950s through 1970s were a product of politics way, way more than a driver of it, and so is the present reactionary judicial backlash. In fact, the biggest thing I'd say you could argue was the courts leading, Roe v. Wade, worked for a few decades, but at the same time set up a ton of resentment that was later exploited to help blow up the whole system around it.
And if you go back far enough, you run up against a violent revolution, also not conducted in court. Although even there it's important to remember that revolutions invariably fail if they don't have huge political support first.
So, if you want to actually do something, go elect some politicians who will clean up the mess. By the way, that doesn't just mean going back to the way things were one day before Trump. It means fixing the long-term institutional decay that let Trump and his manipulators cause so much chaos when they happened to win an election with honestly not overwhelming support.
[By the way, I need to edit this: This particular authoritarian move is relatively bipartisan and represents an attitude that's become depressingly common all over the planet. Nonetheless, if you want to do something even about this, the answer is still political.]