I guess it depends on the source. I always thought the best selling rock album of all time was “Eagles Greatest Hits.”
“When it comes to album sales in the United States, this Eagles’ collection of favorites and timeless classics remains No. 1.”
Wikipedia says it’s “Thriller” - but that could be classified as more “pop” than rock - with “Back in Black” as #2 and the Eagles “Hotel California” at #4. (”Dark Side of the Moon is #3).
Also saw this at another source:
“Biggest selling albums in US History”:
Eagles “Their Greatest Hits (1971-1975)” 38 million
Michael Jackson “Thriller” 34 million
AC/DC “Back in Black” 27 million
Eagles “Hotel California” 26 million
Michael Jackson was pop, even though Eddie Van Halen did the guitar solo on "Beat It".