Yeah, citation needed. I see this everywhere online, often used as a rhetorical device to blame toxic dating culture on irrational female behavior vs reasonable men willing to settle. But I don't think this claim even shakes out in the surveys. I remember having this conversation with a friend, and IIRC we found an okcupid study showing that both genders are generally hypergamous. Dating app dynamics make it so men act slightly less hypergamously than women, but both men and women ultimately try to date up and shoot for the top 20% if they can. People don't want to settle. Anecdotal data point: me - as a man, I still definitely have standards.
Edit: yeah in fact okcupid found basically the opposite to be true https://archive.ph/2017.01.21-154729/https://blog.okcupid.co... "As you can see from the gray line, women rate an incredible 80% of guys as worse-looking than medium. Very harsh. On the other hand, when it comes to actual messaging, women shift their expectations only just slightly ahead of the curve, which is a healthier pattern than guys’ pursuing the all-but-unattainable."