In the blog post for Guerilla's 20th anniversary they have posted updates on Horizon sales figures.
"As of April 16, 2023, the Horizon franchise has sold through more than 32.7 million units worldwide, of which Horizon Forbidden West has sold through over 8.4 million units."
- 8.4m for Horizon Forbidden West on PS4+PS5.
- 24.3m for Horizon Zero Dawn on PC+PS4 and Horizon Call of the Mountain PSVR2 combined.
20 Years of Guerrilla: The Story of a PlayStation Studio – PlayStation.Blog
For comparison Zero Dawn sold around 7.6m in it's first year. So the sequel has sold a bit better in the same time period. I imagine the large majority of sales are on PS5.
Steam Deck Fangirl, Series X appreciator, PlayStation Games freak, Switch 2 Beggar.
Console Launch Aligned Sales Charts