Apparently, it comes from Tik Tok (I personally don't use this social media but this time I feel like they are onto something).
Red Nail Theory means that: "Men are especially attracted to women wearing red nail polish, and that attraction exists because men remember seeing their mothers and teachers wear red nail polish when they were children"
Do you agree with it?
I personally think that if a guy approaches you or comments on your red nails it's because red is simply a gorgeous rich color and a color of passion, sex. That's why many men like red lipstick on women and/or red dress, red anything.