https://edition.cnn.com/videos/cnnmoney/2018/09/13/google-vi...
https://www.theguardian.com/technology/2018/sep/12/breitbart...
That shows that they were emotionally upset, but by itself doesn't give evidence of any concrete action. However it helps to put the other things in context.
For concrete things, firstly, there was algorithmic demotion.
This is a 2017 article that explains their Google's effort to reduce upsetting-offensive content
https://searchengineland.com/google-flag-upsetting-offensive...
> Facebook will change algorithm to demote “borderline content” that almost violates policies (...) The change could massively reduce the reach of incendiary political groups, fake news peddlers https://techcrunch.com/2018/11/15/facebook-borderline-conten...
There were also some outright bannings. Two famous cases:
> In 2016, Twitter permanently banned Yiannopoulos for his participation in a targeted racist harassment campaign against comedian Leslie Jones. In 2017, Yiannopoulos resigned from Breitbart amidst outrage over comments he made seemingly defending pedophilia. That also resulted in the termination of his book deal with Simon & Schuster. Universities canceled multiple speaking engagements, including his 'Free Speech Week,' amidst protest to his ideas on, well, everything. And as recently as last week, Politicon pulled him from the speaking lineup — which was to be his return to the speaking spotlight.
https://mashable.com/article/milo-yiannopoulos-deplatforming...
> YouTube, Apple and Facebook have removed main outlets for conspiracy theorist Alex Jones and his Infowars website, citing repeated violations of policies against hate speech and glorifying violence. Infowars responded by accusing the companies of censorship.
https://www.npr.org/2018/08/06/636030043/youtube-apple-and-f...
Now you may perhaps say that this was all justified. But that doesn't matter, as all I'm trying to do is show that it happened.
It's not implausible that the mostly liberal tech workers decide to not boost "right wing" content, but I'm not going to go down rabbit holes to find out, especially Breitbart rabbit holes where some random HNer said at the door "what you find in this rabbit hole will be true!".