If anybody has sources that definitively prove that men are less likely to underreport more than women even on anonymous studies/surveys, please provide them.

I have a few:

One study found that vignettes portraying a woman raping a man led to a lower likelihood of disclosing or reporting the assault, compared with a male-on-female rape.

Yet another study found that compared to sexual minority transgender/nonbinary people and cis women, cis men were less likely to acknowledge their rape.

One more study concluded that male rape survivors are less likely to acknowledge their own experience as rape compared to females.