I would say that it's linked to the online presence, but that it goes much deeper than that.
Cognitive biases play a key role in conspiracy theories and all those extremist groups that believe in conspiracy theories. These biases are very significant, and not only for extremists, both far left and far right. The biases have been amplified by what Gérald Bronner, a French colleague with whom I work, calls the cognitive marketplace of ideas online. In the marketplace of ideas, we don't have any control. The most attractive proposals aren't true or scientific, but instead revolve around conspiracy theories.
Racism and immigration issues are often behind these conspiracy theories. There has been a great deal of talk about QAnon. Actually, QAnon is recycling old conspiracy theories and modernizing them. This happens in cycles and it's always the same conspiracy theories.
In the case of QAnon, it's about a global pedosatanic cabal. However, I can tell you that, in the 1990s, I studied a group of Catholic fundamentalists called the White Berets based in Rougemont. I don't know whether you're familiar with them.