I think the point is that the resurgence in far-right violence experienced in the UK this summer is linked to them being allowed back onto major social media platforms, particularly Musk's decision to let Stephen Yaxley-Lennon and co back onto Twitter. The article points out that the far-right in the UK don't operate through a central organisation but instead rely on bombarding easily-influenced segments of the population with daily propaganda and misinformation as a means of radicalising them to take violent actions locally - that strategy depends on far-right figures having access to the mainstream platforms that their target audience can be found on.
I agree that is what the article is attempting to say. I'm not so sure if it is really true or particularly important though, and distracts from the actual problem. I disagree that their strategy relies on having access to mainstream platforms, I think the main purpose of their mainstream access is to try to influence our politics with their propaganda.
I don't think people get radicalized on twitter, they get radicalized on an individual basis at the grassroots level in more intimate communities, after doing their recruiting on a more one-on-one basis in places like niche, decentralized gaming communities.