Honestly I'm not a big Lovecraft guy. Like I read synopses of his stories and impressionable nerds being driven mad by wacky weirdo shit seems like extremely my thing, but reading actual stories is like pulling teeth. Maybe he was just that bad of a writer or maybe I don't know English well enough to enjoy his verbose nerdy prose...
I guess there's a point to be made that Lovecraft's stories have reactionary themes and then another point that there's nothing wrong with enjoying art that has a "bad" message.
I don’t even think the overarching theme of “the truth is more horrible than the comforting lies we tell ourselves, absolute knowledge of the world will lead to madness” is inherently reactionary.
Racists read into it and believe the ugly truths are racial truths hidden by a cabal of scheming (((old gods))), but it can also be interpreted that the massive amounts of exploitation and suffering throughout the world would lead to total alienation and madness if actually internalized and understood, and the uncaring inhuman system that drives the horror machine forward.
Obviously his xenophobia is rampant in his work and a part, but I would say it is not defining. Xenophobia is fear of the unknown other. Lovecraft obviously also includes themes of the fear of the known, that truth is maddening, which is more of a fear and hatred of oneself.
As I've said I'm not much of a Lovecraft guy, but people generally point out fear of miscegenation and of racially removed other as his reactionary themes.
He was basically grillpilling before that was a word.