Toxic masculinity is a term used by feminists in order to account for the problems allegedly caused by men. Sometimes it is used to describe violence and sexual crimes towards others enacted by men.  This discounts the violence, particularly domestic violence and sexual violence, which is just as likely if not more so to be enacted by women. Other times it is used to refer to the tendency of men to avoid acknowledging their emotions. Though this idea is certainly more factually grounded than the other one, it neglects to take into account the biological tendency of men to express their emotions through actions rather than discussions, as well as the fact that gendered male behaviors are often more encouraged by women than other men. Some sources even conflate the two clearly unrelated phenomena.
In general, the term toxic masculinity is deliberately incendiary and intended to shut down rather than facilitate discussion. The people who came up with that term were not interested in helping men and boys.
The term 'toxic masculinity' is toxic.