I'm not sure if any studies accurately measure the subject content, and it also seems like it'd be easy to get any result you want by tweaking the experiment parameters.

I can tell you that from my own life experience and what I can recall, it has certainly felt like a shift in content. All the anti-white stuff, the social justice stuff, the pro-censorship stuff, etc. It existed before in tiny bubbles like Tumblr, but it was during the mid 2010s that the major news sources started adopting those viewpoints too.