Probably the most useful book ever written about topics adjacent to capital-R Rationalism is "Neoreaction, A Basilisk: Essays on and Around the Alt-Right" [1], by Elizabeth Sandifer. Though the topic of the book is nominally the Alt-Right, a lot more of it is about the capital-R Rationalist communities and individuals that incubated the neoreactionary movement that is currently dominant in US politics. It's probably the best book to read for understanding how we got politically and intellectually from where we were in 2010, to where we are now.
https://www.goodreads.com/book/show/41198053-neoreaction-a-b...