Millie Bobby Brown brought out some close friends and family together for an intimate birthday party ... and, if those David Harbour rift rumors weren't dead before, they certainly should be now.

The actress turned 22 earlier this week ... and the party raged at Maison Close in the Soho district of New York City Friday night, where our sources say the group congregated into the early Saturday morning hours.

Millie and her man Jake Bongiovi looked like the toppers of a wedding cake ... with Millie in a chic white dress -- while holding what looks like a Union Jack, the UK's flag, and Jake dressed up in a thick black coat and white dress shirt with a frilled collar.

Among the other attendees were Millie's mom and grandparents, reality stars Whitney and Conner Leavitt, director Shawn Levy, "Stranger Things" villain Jamie Campbell Bower ... and, Harbour, who we're told arrived early and exited late in the evening.

Harbour kept a low profile in a black baseball cap ... but that coat and thick beard are instantly recognizable.

As you know ... rumors that MBB filed a bullying and harassment claim against Harbour swirled right before the release of "Stranger Things" season 5 -- rumors Brown repeatedly denied.

The two were all smiles at red carpet events for the show ... and Millie later said she felt more comfortable and safe while acting with Harbour.

"Stranger Things" is over ... but it looks like this friendship will never end!