Trump is upset that the Supreme Court said people arrested by ICE require due process before being deported.
Keep in mind that if Trump wanted the _legal_ power to tighten immigration laws, he could have supported the bill championed by his Congressional allies last fall. He did not.
If immigration was actually as large a problem as he claims, he wouldn't need to lie so much about it. If he thought his plans would be popular and legal, he would've made them public - if he had any.
Instead he publicly disavowed Project 2025, which was filled with his own supporters - many of whom joined his Administration despite him saying they wouldn't. But he's trying to implement their policies anyway.
And then of course, there's the matter that the "due process" Trump derides is enshrined in the US Constitution, and (among other things), it protects US citizens from being branded "illegal immigrants". "Due process" also allows there to be a distinction between "legal" and "illegal" immigrants.
Trump doesn't want to be able to _legally_ deport more people. He wants to be able to deport _anyone_, citizen or not, legal immigrant or not, on a whim, without showing evidence, and without giving them time to respond. He wants to make it clear that the law is whatever he wants at the moment, and that he can take any action, at any time, against any person, for any reason.
Immigration is just the gateway issue, the one on which he has the most support. But he's had multiple opportunities to show that he _wouldn't_ exercise these powers against citizens, legal immigrants, and people who were never a threat.
In every case, he has refused any form of restraint.
He is an authoritarian, and he's not even trying to hide it.
He claims the power to deport _you_. _Now_. For any reason. Don't let him.