Short Answer: Naturally, of course they can.
Long Answer: Yes! The assumption that feminism could only be open to women makes two very fatal and inaccurate assumptions, that only women suffer under a system of such stark gender inequality, and second, that women are the only victims of misogyny. Both are untrue. There are men who are victims of misogyny, such as nonbinary masculine folk and trans men.
Men can be feminists, the movement for eradicating gender inequality requires all types. There’s only one condition to men being feminists: When they identify as feminist, I am going to be critical when they espouse ideas that are antifeminist or participate in casual sexism, and hold them to a standard that I would expect from someone who is a feminist.
If you think this is unfair, I’ll let you in on a secret: I act the exact same way towards women who are feminists. If you don’t believe me, I’ve got posts on this blog showing criticism of women who identified as feminists but failed to live up to gender equality ideals or completely diluted/misused the word “feminist” to the point where it was unrecognisable. Nobody is exempt from this because of their gender.
Seem fair now?