The Proud Boys were heavily infiltrated up to and including Enrique Tarrio. Atomwaffen was entirely astroturfed. The libertarians entrapped in the Gretchen Whitmer case. The "right" has a long history of FBI infiltration--klan meetings being comprised entirely of feds trying to bust each other has been a running joke for decades.

The "left" is similar, but it's not usually the the FBI these days AFAICT.

The Atomwaffen are legitimately a gang that has killed several people

They were legitimately a group of mentally ill losers sharing edgy memes. The FBI got involved (see Josh Sutter) and began producing those well-crafted propaganda materials, including videos featuring actors wearing identical clothes to actual members. A lot of them got spooked and jumped ship. Those who stayed were literally drugged as part of "occult initiation" rituals, and, yes, some were finally convinced to carry out murders.

I've always felt like the fact that they seem to constantly be thoroughly invested in the right wing groups and let them persist, while they barely infiltrate the left and done everything they can to destroy them asap, really suggests theyre not so much infiltrating the right wingers as much as taking control because they actually support the underlying ideology....

But maybe that's just something I see and is just a perception issue.