Just as an example, I had a quick look at the current UK top 10 fiction best seller list. There isn't a single definitive list so I actually looked at two different lists, the WH Smiths list, and the Sunday Times list.
All the authors in the Sunday Times top 10 are white. There's one American author on the WH Smiths list who is half-Korean and half white, the rest are white.
All the authors on both lists are either British or American.
Nearly half the British authors in the Sunday Times top 10 went to public school. (Not just privately educated, actual public school.)
The WH Smiths list is 50/50 male and female, the Sunday Times list has 6 female writers so slightly female-dominated for this week.
I haven't read all the books on the list so I don't know whether they have non-white characters or not, but all the authors are white except the one half-Korean author, so clearly we either have white authors writing books with only white characters (without criticism or controversy) or white authors writing non-white authors (again, without criticism or controversy). For example Richard Osman has two books in the top 10 right now and the main characters in his series are two elderly women and a gay Asian man. I've not seen a word of criticism anywhere suggesting that Osman is wrong to do this when he's a white heterosexual man. His books are insanely popular and he's pretty beloved as a TV personality and author.