You're not wrong. If the President does not follow a federal law, he is not performing an official act, and he is not immune from criminal liability.
If he chooses to continue to ignore the law, the solution isn't the courts. It's the Second Amendment, which was added to the Bill of Rights as a check on exactly this (though the Founders intended for it to be exercised through the States' militias, not the citizens directly, based on the text of the first half of the amendment).
Before resorting to violence, the remedy is to impeach and convict the President, and, failing that, elect a replacement President. Only if the incumbent fails to cede authority should further consideration be taken.
And, to be honest, I’m not really sure that a bunch of unorganized wingnuts that slobber all over their big-man toys are going to prevail over the National Guard, if the latter remain loyal to the President, and a lot of innocent lives will probably be lost due to militia incompetence.
Biden didn't ignore immigration law. He executed it. He arrested more immigrants than Trump did during his first term. Republicans simply disagreed about how he was executing the laws because they wanted political talking points (and notably at Trump's urging, shot down a number of proposed immigration reforms that would have reduced illegal immigration, cut down on the asylum loophole, and make it easier to deport immigrants with criminal records...Laken Riley was killed by an illegal immigrant who was still in the country because Republicans blocked the laws that would have deported him.).
Trump isn't following the laws at all. He's simply issuing "executive orders" without regard to the powers or limitations of the executive as stated by the Constitution or the U.S. Code. Almost every single one of his executive orders during his second term violates a Constitutional prohibition in some way, and now that the initial shock to the system is over you're seeing judges overturn almost all of his orders...Even judges appointed by Trump during his first term are starting to overturn his executive orders.
So Trump's response was to call for the arrest of these judges. And to hint that violence would be appropriate way of removing them from.
What's good for the goose is good for the gander. If Trump gets killed by a mob this term, it's going to be because he kept suggesting that violence was the way to deal with his opponents.
If he chooses to continue to ignore the law, the solution isn't the courts. It's the Second Amendment, which was added to the Bill of Rights as a check on exactly this (though the Founders intended for it to be exercised through the States' militias, not the citizens directly, based on the text of the first half of the amendment).