There has been a huge influx this year with the amount of sites that simply scrape SO and then have the exact content on their site. It's a pain, and there is no official way to remove them.
I thought that this was a massive nono from Googles side, has something changed?
I've been using this uBO filter since someone recommended on a different thread and it's been great at removing those annoying sites from search results: https://github.com/quenhus/uBlock-Origin-dev-filter