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We hate what we fear. Study Finds That Homophobic People Are Actually More Likely To Be Gay

Netta Weinstein, a lecturer at the University of Essex and the study's lead author, said that these individuals "may be threatened by gays and lesbians because homosexuals remind them of similar tendencies within themselves".

There are a bunch of studies like this. I don't know if anyone has done a systematic review to bring them all together in one read.

It's important to note that there is no implication that every homophobe is secretly gay, just statistically more likely to be than less performatively toxic individuals. Some homophobes are insecure in their masculinity (or femininity) for other reasons and so hide behind a parody of what they think masculinity (or femininity) is.

The other important (and AFAIK, consistent) aspect of these studies is that they were taught to hate themselves:

"Those people who have such discrepancies, who have really a split between their unconscious attraction and what they consciously say about themselves, are more likely to come from authoritarian homes."

"If you are a parent who really believes your child should be straight, and when you use whatever means you can to convince them them that they're only good and worthy if they are, that would be very controlling and it creates a lot of conflict in the child."