It was nothing until Steve Bannon got involved.

Gamergate was a swell of support for scum like trump and bannon

My understanding is that there were genuine journalistic concerns with regards to Anita Sarkeesian, but then the narrative ended up getting twisted into a sexism thing when sexist gamers got involved. If I recall correctly, the initial issue was that the editor appeared to not be impartial when selecting who to write for what topic, and people believed that the perceived partiality was because of the fact that Sarkeesian and the editor were in a relationship. It's a clear conflict of interest, but nothing major. What would have/should have been a minor journalistic scandal devolved into creepy incelposting.

Which really muddied the waters, because it also caused many regular people to dismiss the initial, core concern that the journal did have a conflict of interest.

While Sarkeesian definitely did not deserve the harassment, I think it should also be noted that she is a somewhat problematic individual. There was scandal that came up back in 2020 or so where she accused a game developer/ex-boyfriend of being abusive, which is generally acknowledged to have led to his suicide just several days later. But later reports revealed that many of her accusations were incompatible with evidence, and so it's unclear how much, if any, of the accusations were truthful

Edit: mixed up two people. I'm unsure how much the wires got crossed, and I don't have time to fact check myself right now. Please take this comment with a huge grain of salt

I went so far as to download archives of reddit from that time period. But I get completely lost when people start using "gamergate" and "anti-gamergate" as surrogates within that conversation. They both start getting used as subject, adverb, adjective, political stance, but it's still not clearly.defined to an outsider.