just got an Oscar nomination for his role in "Barbie," but the lead actress herself -- -- was left out in the cold ... and yes, people are pissed.

The Academy Award nominations were announced Tuesday, and RG was on for Best Supporting Actor -- alongside Sterling K. Brown, Robert De Niro, Robert Downey Jr. and Mark Ruffalo. The black sheep in this group, you could argue, is Ryan ... who played Ken.

It was a goofy and even goofier performance -- and yet, Academy members seem to think he acted his ass off and is worthy of recognition .

.. something insiders predicted for months.

Now that it's happened, a lot of folks are happy for the Ry Guy -- but even more are angry on behalf of Margot ... who got snubbed this morning, and didn't receive an acting nomination herself. To be fair, there was a lot more buzz around Ryan ... but there's still outrage today.

The argument here for MR basically amounts to ... she freakin' carried that movie, and she showed some range in the titular role as Barbie, going through a roller coaster of emotions.

Some are chalking it up to good old-fashioned sexism/misogyny ... and are crying foul.

While Margot missed out, her costar didn't -- she was nominated for Best Supporting Actress, and 'Barbie' itself is up for Best Picture. It's just Margot who got screwed.

So, here's the question ... do you think she deserved to get an Oscar nod, or not???