HK man arrested for possession of flag

It looks like the most concerning expansion of power here is that under the new law (download the PDF and read for yourself, Chapter 3: "Offences and penalties"), advocating for or organizing events for the separation of Hong Kong from China is an offence.

As is, potentially, someone donating funds to persons organizing such events or publishing such opinions. "...A person who incites, assists in, abets or provides pecuniary or other financial assistance or property for the commission by other persons of the offence..." That is quite an expansion.

The penalties range from < a few years to > 10 years prison.

The rest of the law is not that different from anti-terrorism and sedition laws that other countries have.

I'm sure it will be of significant concern to see whether protests for the freedom of speech and related civil activities (aside from HK independence or separation) get swept up under this law or not.

Op, did you even read the article? It says the police raising a new signalling flag as a warning. It has nothing to do with anyone possessing a flag and being arrested.

This is what communism does. A few controlling the many, making everyone equal in their misery.