1) Ngo is not white. I read his book and saw nothing there about "white supremacy". [edit] Ok, except maybe a biased take on Arbery murder in particular. Which doesn't really have much to do with anything systemic, or with most of the rest of the book. He's very clearly a classical liberal, either conservative-leaning or considering the right to be the lesser of two evils.
2) Proud Boys leader (until recently) was Black. Proud Boys are far-right, sure, but you really should stop calling everything you disagree with "white supremacist".
3) Ngo, as far as I can tell, merely used Proud Boys as a "resource" for his own safety and/or under "enemy of my enemy is my friend". As someone born in a socialist country, I cannot really blame him - far-right is evil, sure, but far-left is at least as evil, and I would argue more evil.
4) In any case, the statement "noteworthy by documenting the excesses of the far left" is true. The only framework under which one would need to mention that "but he also offended woke sensibilities in an unrelated/tangentially related matter" is the woke cult, the one that the author (and Ngo) do not belong to. For most of us, it is sufficient to let an arbitrary fact, or an accurate description, stand by itself.