The Lemmy software stack was literally created by political extremist. (Not activity pub as a whole) At least one of the lead developers is a tankie. Though is that really more extreme than most capitalist? Not really. Both are pretty extreme. Resulting in heavy centralization of power and resources to the detriment of the average person.
In general Activity Pub as a whole is definitely more left leaning and anarchist. Which is a good thing. If you think otherwise. Why would you think mutual aid, community, and smaller more accountable governance etc is a bad thing. After all it's what extremely far right groups like the Republicans in the US pretend to stand for while delivering the opposite.
No one in society is politically neutral. And different isn't necessarily extreme. If you can acknowledge that. You might find you have more in common than you think.