For people who are new to this topic and find it to be surprising: This is not new. There is a term for this called "echo chamber":

https://en.wikipedia.org/wiki/Echo_chamber_(media)

I have observed this trend happening on Internet since 2014 and written about it in my blog:

https://paradite.com/2014/11/11/internet-polarized-society/

Previously it was more for closed communities like reddit and Facebook groups, but seems like now it is also substantial on open platforms.