I'd start by being wary of anything that says it's 'for men.' The male parts of reproductive medicine/endocrinology/etc. can be studied but real understanding in that area is college/post-grad level courses of material. Almost anything approachable will be over-simplified unless you really dive in. However, on the social side, (brains, emotions, support networks, etc) it's usually a bad sign when the source says anything is exclusive to men. Most philosophy, psychology, sociology, emotional intelligence training, etc. is not served by framing it based on sex, and a lot of stuff that is framed that way tends to be propagandistic in pretending this or that understanding of sex-based social norms (a.k.a. gender) is the one true way. Studying psychoanalysis can be good, and i can recommend the Quarantine Collective on youtube as a nice place to learn about philosophy and a little bit of psychoanalysis, often presenting a secure, non-misogynistic masculinity. For emotional intelligence, it's more about practice than study but Heidi Priebe has made some good explanations, though watch out for the woo in Jungian thinking. And while it might sound strange to some, finding a good (for you) teacher for vipassana and metta meditations can be very helpful in understanding yourself, regardless.

I know of two things that I thought were good and they are intro level and maybe a bit more advanced but interesting, so I’ll just post the important bit, albeit reworded, of my other comment for visibility in case it helps anyone or whatever.

The first is Why is the Penis Shaped Like That? and other reflections on being human by Jesse Bering. It’s a sort of lighthearted approach to male bodies and other weird quirks of being alive, written by a research psychologist, as well as a columnist for science communication publications like Scientific American. He’s also a gay man who really likes penis stuff. I cannot not mention that, because he himself mentions it as part of his credentials within various articles.

The second is a book mostly about how penis things go wrong, testicular torsion, various kinds of erectile dysfunction and how they get fixed and stuff, it isn’t strictly informational, more like case studies that have been anonymized. It’s called Why Men Fake it, the totally unexpected truth about men and sex by Abraham Morgentaler, a urologist and sexual dysfunction specialist.

Both of these are good not super scientific explorations of things you may want to know, but don’t. I learned a lot and enjoyed the process.

Most scientific studies have been done on only men, that's why airconditioners always make rooms too cold, because men bodies generally prefer a few degrees less. It's actually an issue.

I'd say the Modern Wisdom podcast. While it's not explicitly marketed for a male audience, that's still the majority of the listener base, and even though much of the discussion about behavior and psychology applies equally to both genders, it's still mostly explored from the male perspective.

mirrors

The Demi Moore movie Striptease. At least I discovered a lot about myself as a young boy watching that film.

Therapy

what some of the more useful resources are for men to learn about their bodies

idk, I just started playing with my dick one day and that was the extent of it.

hormones,

Testosterone good, rawr!

brains,

I know I shouldn't try to poke it through my nose...

emotions,

What are those?

support networks,

What, like a jock strap?

Really, most of these things I learned about through some innumerable number of sources I can't possibly remember now, which were not particularly gendered. Idk, just read shit?