You can buy 2-slot 4090s.
https://www.reddit.com/r/nvidia/comments/10f750o/blower_style_rtx_4090_2slot_%E3%83%BC_photos_and_a_couple/
You can buy 2-slot 4090s.
https://www.reddit.com/r/nvidia/comments/10f750o/blower_style_rtx_4090_2slot_%E3%83%BC_photos_and_a_couple/
Probably existing designs from factories that produced legitimate blower 4090 coolers before the ban.