This could to do with the levels of proof required. Sometimes a court or prosecutor might say that there was probable cause to justify the arrest but not to take to trial or convict. So it doesn't necessarily mean the person wasn't a danger, just insufficient evidence for an extended denial of rights.

That;s the magic word right?? "probable cause".  So they can do what ever they want.

That;s the magic word right?? "probable cause".  So they can do what ever they want.

No.  Probable Cause is the standard for making an arrest.

To establish probable cause, police officers must be able to point to objective circumstances leading them to believe
that a suspect committed a crime. A police officer can’t establish probable cause by saying only something like,
“I just had a hunch that the defendant was a burglar.”

Judges, not police officers, have the last word on whether probable cause exists. A police officer may be sincere in
believing that the facts establish probable cause. But if a judge examines that same information and disagrees, then
probable cause does not exist (or did not exist, if the question is being decided after an arrest).

Note that probable cause may have existed at the time of an arrest even if the defendant didn't actually do anything
wrong. Put differently, an arrest is valid as long as it is based on probable cause, even if the arrested person is innocent.

Key phrase:  "police officers must be able to point to objective circumstances leading them to believe that a suspect committed a crime."

Red flag laws, by definition and intent, do not wait until a crime has been committed.

You can't have probable cause if a crime has not been, nor is not about to be, committed.  Even if you want to argue the crime is related to firearms laws (mentally ill owner in possession of firearms), that's called bootstrapping.  There needs to be articulable evidence of mental illness.  "Acting crazy" is not evidence.  If it was, half of Congress would be committed.

A person is a danger or isn't

If they don't have guns that doesn't make them any less dangerous

Well maybe a little less dangerous but certainly not harmless.

That;s the magic word right?? "probable cause".  So they can do what ever they want.

Probable cause is a legal term for a certain level of proof and has been standard in court for a long time.

So you report to the police that someone assaulted you and you identify the person who did it to the officer the officer has probable cause to make an arrest. This is a very simplified scenario just to illustrate it.

Probable cause is a concept that can be difficult to nail down with a single universal definition so there is a certain flexibility for a judge to weigh in on. One of the standards is what a reasonable person would think. Now if you are hinting that it can be abused, yes sure, but that is not unique to firearms and red flag laws. But it cannot be just whatever they want it to be.

https://www.law.cornell.edu/wex/probable_cause

Probable cause is not limited to criminal cases though, it is also used to determine whether there is enough evidence or information to justify a civil lawsuit. So there does not have to be evidence of a crime for probable cause to have been found.
https://legal-dictionary.thefreedictionary.com/Probable+Cause