Due process applies when you've been accused of a crime. When you've been accused of a crime, the state has the power to, for example, remove evidence of that crime from your possession, but only after due process, i.e., a warrant signed by a judge permitting the state to search for and seize said property. So the state may not take your property in connection to an accusation that you are plotting a crime (which is a crime in itself) without first giving you an opportunity to face your accuser before a neutral judge and contradict him, along with the assistance of an attorney. That's due process for a taking.
The problem with the Red Flag laws is that they have to do with, essentially, an accusation by the state that you are plotting a crime (or, due to mental illness, are on the verge of committing a crime), but they skip over the requirement of a sworn statement to a judge that evidence for this exists that makes it more likely than not true. That sworn statement is crucial, because if fabricated, it places the accuser in legal jeopardy, which makes it more reliable, because much less likely to be frivolous.
I’m not trying to argue whether red flags are good or not, I don’t like them. But all the ones I’ve seen require an affidavit like a protective order or a warrant.
