It's not wanting to get strong that's toxic, it's a fine goal. Most basics of masculinity, like>A man should be as independent as he can be>A man should work and earn a living>A man should aim to be strong
Aren't that objectionable at face value, and in a vacuum are probably all good things.
Toxic masculinity is the flip side of all of these coins though coin, the implications that come as a result of creating pressures to meet those goals.
For example, if someone believes >being strong makes you more of a man
there's a toxic inverse, >someone who is not strong is less of a man.
Which leads to problems like bullying in schools, macho stupidity (Crushing cans on your head because you can), and pushes guys who don't care about getting strong towards doing something they don't actually care about just to please other people, which shouldn't be what ANYONE wants, including guys.
People generally believe in toxic inverses like that whether they're aware of it or not. Through no fault of their own, most people aren't, because it's like they're fish in their culture's deep sea, they wouldn't be aware that there's the water around them if they're unaware of the air above.
These toxic inverses create societal pressures that lead to things like rape (Toxic inverse of "A man should have sex frequently"), gang violence ("A man should be master of his domain"), and gender discrimination in the workplace ("A man should be a leader"), and unhappy marriages by people doing it for the wrong reason with the wrong people ("A man wants to find an attractive woman")
The goals aren't bad, the toxic part is the structural pressures caused by society evangelizing those goals in backwards and unhealthy ways. Awareness goes most of the way towards not doing it.