I think without a doubt there's numerous examples of men and boys being systemically affected by sexism. Schools and courts are infamous examples with how horribly misandrist both are, and a classic example is men being required to register for the draft and facing legal action if failing to do so. Also much of society and even governments failing to recognize male victims of domestic violence/abuse, rape, etc. (especially by women, when male victims have the stigma of being deemed "unmanly" if harmed by a woman) and how misandry's existence is still largely unrecognized or even denied. Also a horribly misandrist "organization" like UN Women even being allowed to exist. I'm sure there's other examples I'm forgetting but these are the mains that stick out. "Believe women" is another I can think of, which blatantly denies due process and also brushes aside false accusations, and makes it harder for both genuine male and female victims alike to get help.

Sexism is terrible no matter which direction it swings in, but to deny men can experience it and that there's no systemic sexism affecting them is plain ignorant, stupid and downright infuriating to claim. Sexism is wrong either way but when it's against women it's frequently condemned and criticized, not so much against men. Men being affected by it by individually and systemically continues to be swept aside, and I hate it so much.

And to be clear since so many people are quick to make assumptions about political leanings which is always annoying, I'm mostly liberal and left-leaning (but not a certain four-letter W-word). It's so cringey to me how many people associate being liberal in anyway with hating on men or being ultra right-wing if advocating for them. To me there's nothing political about pointing out the simple (and often overlooked and ignored) fact that sexism also badly affects men and on a systemic level many ignorantly deny. I think this is something the moderate and open-minded folk on all sides of the spectrum can agree on.