It is being told to women in high school and college as the reason they aren’t allowed to take hard physics courses.
If you were referring to the 1950s, or maybe life on some other planet, I think I would be more inclined to believe this. From everything I am seeing in the real world of here and now, all things STEM are practically being shoved down girls’ throats whether they have the least interest in them or not. And as for active discouragement, you might want to have another look at who is attending college and who is graduating with more degrees in general. Hint: they are not male.
There is no patriarchy. There is no sinister plot to hold women back. Fields that are “male-dominated” are that because women plain aren’t interested in them and if they are but still are in a minority, people bend over backwards to be seen being “inclusive” of them. I challenge you to find any two men who would support each other publicly in ANY position regarding women and career choices, other than the damseling-by-proxy posture men today use to prevent themselves being driven out over made-up harassment charges.
Personally, I think you are seeing sexism around every corner because you want to, because you take half-century obsolete narratives about women’s place in society at face value, and because it is fashionable to call a nakedly matriarchal, woman-advantaging way of life “patriarchy”, and then go looking for the most isolated examples to extrapolate into some antique secret-handshake conspiracy by men against women.
And, again, I ain’t buyin it. I have yet to see a grown woman in over fifty years who ever let anyone, much less any man, “actively discourage” her from doing whatever it was she set out to do. And if that is all it takes to turn anyone back, I daresay they have more of a character problem within themselves than any gender one from “society.”
As with all things feminist, you are under-rating women, and pitching them a victim narrative that is of no use to any adult with the grit and determination to see goals through. Instead you will attract mediocrities looking for a free ride, and more than happy to blame their own shortcomings on some nonexistent prejudice holding women back.