All of the above are misuses of "brownshirt" by people who heard the word and, like I did, neglected to check a dictionary, thereby unwittingly invoking a Nazi reference.

https://www.merriam-webster.com/dictionary/brownshirt

There doesn't seem to be any evidence that "brown shirt" nor "brownshirt" was used a metaphor for a person in any kind of role before the 1920's, when it came into use in reference to the Nazi storm troopers.

The "digital brownshirt" term was likely coined by someone who knows what "brownshirt" means; their intent is to express the idea that right-wing bloggers are like Nazis of the digital age. That use does not assigns a new meaning to the "brownshirt" constituent word.

I have seen the word very rarely myself; I passively learned about it decades ago, and have not seen it used since. I used it about once or twice myself. Since that time, I have become more fastidious about looking up unknown words (which has become easier, thanks to mobile devices!) It's highly probable that the person I saw using the term decades ago knew that it was a Nazi reference.