None of rhe conservatives I grew up with nor any that I have encountered in many years of political activism ever held any views like that. And such views are utterly incompatible with conservatism.
I agree that no self respecting conservative would hold such views.
All I can tell you that on a many a summer night as a child at Lake Tahoe,I sat around as adults sipped gin and tonics and warned of racially”inferior”people taking over.Almost all of these folks were good Republicans.
I agree with you these views are repugnant.But they were commonplace in my upbringing.
Best example is probably the reference to the book Tom Buchanan is reading in The Great Gatzby about the dark race population explosion. It is very subtle - but true.