https://spunout.ie/life/bullying/what-is-toxic-masculinity
https://www.medicalnewstoday.com/articles/toxic-masculinity#what-it-is
https://greatist.com/grow/toxic-masculinity#What-is-toxic-masculinity?
That took all of a few seconds to look up... But if you really want my opinion, it boils down to a gross distortion of what masculinity is supposed to be. Men are supposed to be tough - Toxic Masculinity demands that we be emotionally and physically invulnerable. Men are supposed to be competitive - Toxic Masculinity demands winning at any cost. Men are supposed to be strong - Toxic Masculinity demands that we prove it with violence. Men are supposed to win the hearts of the women they admire - Toxic masculinity demands that we bed every woman who will spread her legs. It's "maleness" dialed up to ridiculous and poisonous levels.
Because being Gay and Feminine is the opposite of being manly, those who are toxically masculine feel the need to constantly prove to themselves and to others that they aren't girly or gay. This means violence - both against LGBTQ+ and women. It manifests not only as literal violence but also sexual harassment and blatant sexism.
As a straight cis man, I find toxic masculinity to be childish and asinine. I don't need to engage in a pissing contest to prove that I'm a man or treat others like shit just to stroke my own ego and assure myself of my "manliness." I don't pretend to be something I'm not just to give the impression that I'm somehow tougher, stronger, or manlier than the next guy. I stand up for those who are different than me - both in their sexuality and in how they express their gender - because the only thing I feel I need to prove is that I'm a good person.