I've read the Atlantic article & Signal messages twice, top to bottom. Most of those on social media ringing alarm bells and repeating talking points have not.
Should Goldberg have been added to the chat? No.
Did Goldberg gain access to "secret" information? Kind of. He found out we'd strike the Houthis two hours early.
What Goldberg & the Atlantic are calling TOP SECRET "war plans" is a massive embellishment—any butterbar fresh out of ROTC could tell you that. These aren't war plans. These aren't even school board notes.
They're "Ok, we're ready to do that thing everyone knew we were going to do? Yep? Neat. Also Europe sucks."
Watergate this is not. It's a final, informal check-in after things are already planned/assigned.