It took me ages to deal with this, but I did in the end. After a point, I realised that most of the people and pages who came up were repeating quite regularly (I have about 280 friends). So every time a post like this came up, I clicked on the little drop-down menu in the upper right corner of the post and clicked "Hide All From [Friend's Friend/Page].

I spent an hour going down my feed and doing this on the first day, and I noticed that it made my feed significantly better. Didn't spend any more time doing this, but for the next few weeks, whenever that sort of post appeared, I clicked "Hide All From...". Sometimes, rather than the page itself, there will be an option to hide all posts by whichever social media post aggregator app was responsible for showing it to you (these often post for multiple apps/pages), and that's a bit like killing 10 birds with one stone.

In the past, I had to wade through my entire feed to find any posts by friends or pages that I actually follow. Now, I almost never see these sorts of posts - maybe two or three a day at most. Undoubtedly, it's removed some content that I would otherwise have seen (e.g. friend shares an article from a page that I have blocked), but for the most part you still see everything that you actually want to see.