Removing doubt about what? That people on this platform do not agree with his politics? (article is paywalled so I can only comment on the first few sentences)

Incognito mode.

For what is worth, their methodology also looks flawed and paints an exaggerating picture.

If anything I'm not convinced this doesn't just show that Facebook is mostly used by old people, so there's a lot of interacted with right wing or whatever content. I personally see none of it, and very little that's politically charged in general.

That's correct, but sort of missing the point. Facebook isn't deliberately training people on far right conspiracies. But those conspiracies happen to do a really (really) good job of evading what controls exist and end up being presented as "suggested content" to a bunch of people who, while ideologically susceptible to it, wouldn't ever see it otherwise.

And it's a real problem, because this garbage is just swimming in deliberate untruth.

And it's asymmetric. There is leftist lunacy in the world too, obviously, but it doesn't end up being presented to people on Facebook just because they clicked on a climate change link or liked a post about racial justice.

But if you're a retiree who follows your local evangelical church? Your feed is now telling you that masks don't work, that the government is conspiring in one of various Mind Control theories to control your life, that your relatives (the ones who click on the climate links) are already compromised.

It's really, really bad. Just try it. Go to facebook and interact with some totally mainstream right wing entities. Churches, republican party candidates or organizations, the local gun range. And watch what you start seeing.

Don't worry I can see plenty of far-left stuff a few accounts away on Twitter so I can easily imagine the right version.