Amber Heard was indeed sidelined in the new 'Aquaman' movie -- just as an ex-WB honcho confirmed under oath last year -- and the word is ... she's barely even a side character.

"Aquaman and the Lost Kingdom" -- the sequel to the 2018 superhero hit starring Jason Momoa -- just got released in theaters this weekend ... and there's a lot of bad news in terms of box office and reviews, but perhaps the most interesting is Heard's screen time.

According to Business Insider, AH only appears on camera for about 20 minutes or so ... and while she does talk in the film, it ain't very much -- just a measly 11 lines apparently.

BI says Amber shows up for a few action sequences toward the beginning and the end, but she's largely removed from the main story ... even though her and JM's movie baby serves as a central plot point. Some of the lines she reportedly delivers are also pretty laughable.

Here's some of her dialogue ... "There haven't been outbreaks like this in ages. Why now?" ... "They raided the storage vault, we can't let them get away" ... "Where's Jr.?" ... "No!" ... "I sense something in the water" ... "Thank you." There are other lines, but they're also minimal.

Instead of Amber taking center stage, Momoa and Patrick Wilson end up teaming up and leading most of the film. Yahya Abdul-Mateen and Nicole Kidman are also in the mix.

Not surprising that AH was downplayed -- that was being telegraphed dating back to 2022, when she was on trial after Johnny Depp sued her. Walter Hamada -- the ex-Warner Bros. boss -- got grilled in a deposition, and explained the studio decided to sideline her based on a lack of perceived chemistry between her and Momoa, and wanting a different story.

Of course, Amber's team suspected this was because of everything that was going on with Depp at the time -- but the studio denied that. In any case, she's an afterthought in the film.

Once JD scored his W in the trial, many vowed to boycott the film if she wasn't dropped from it -- but at this point, it's hard to tell if the Amber factor really played into the box office numbers thus far ... which aren't all that great, despite the flick being #1 right now.

'Aquaman 2' is on pace to make about $40 mil through Monday ... crappy by superhero movie standards. With that said, it'll lead the holiday weekend pack -- so ... congrats?

BTW, no sign of Amber for the press run on this film ... which was about as low-key as you can imagine, and didn't even have an official premiere. WB/DC's ready to turn the page.