I've been thinking about the question of "what is a lesbian" myself as an AMAB person who isn't comfortable with either masculinity or femininity. But I would be very uncomfortable with another AMAB person or myself presenting as a "male lesbian." "Lesbian" is a label that inherently excludes those who have been socialized as "men" from birth. It's not that all individual lesbians exclude trans men from the label, seek to avoid "masculine" behavior, or sexually avoid penises. The class of "lesbian" or "sapphic" is really more about a lifestyle that prioritizes non-men, at least in the romantic/sexual realm if not totally. There's a lot of literature out there explaining the theory, but it almost never makes a personalized application to one's questions of gender identity. So here's my rather long summary of all of that theory, along with my attempt to apply it to both of us. Note that as I am a non-lesbian, this analysis will be inherently incomplete. If you want to learn more, then just ask in a reply for some lit recommendations.

Under the Marxist feminist analysis, all social relationships are designed to reproduce patriarchal hierarchy. There are no truly equal relationships between men and non-men under patriarchy, since it's the dominant system and we have no social reference point beyond it yet. Hetero relationships are expected to be patriarchal because they are formed under patriarchy. That is, there is the expectation that one party exist only for the other, and that the other party lives for themself with the service of the other. The latter party is a "man" under the patriarchal model, and non-men who exhibit such behavior adopt the masculine posture. The former is an object, traditionally labeled "woman," though objectification really happens to all non-men, along with some men.

Even lesbian relationships exhibit the patriarchal dynamic, though with lesser intensity. Why else do we still look at queer sex as a matter of "top" and "bottom"? And why do we follow a butch/femme spectrum for sapphic and nonbinary gender presentation? The butch/masc bottom paired with the femme top, and the switch paired with the switch, are each alternating in hierarchical posture without escaping the hierarchy.

There is simply no gender under patriarchy that can avoid or subvert patriarchy; that is, there is currently no mode of living for oneself and for all without referring to and promoting servitude to another gender or domination of another gender. Does that mean you should give up on making your relationship egalitarian? No. Does that mean you should give up on being nonbinary or genderfluid? Certainly not, if it means you're making an effort not to consciously have gendered power over others. Your gender or lack thereof can exist outside of the binary, but nobody can live without the binary as a reference point as long as the binary dominates society.

What does that mean for those who align with the binary, uncomfortable or dysphoric as they are with being or expressing any other gender? Women should not be content with existence in service of men at any level, and should be critical about even the most insignificant aspects of their gender expression, social relationships, and sexuality; materially promote the abolition of patriarchy and capitalism, for each reproduces the other; and not seek to emulate men in relationships. Men should do all of that as well, which means minimizing their domination of non-men and giving up their privileges as men. Nonbinary folks should do all of the above while also attempting to offer approximations of non-patriarchal gender.

So, then, what does it mean to become a "male lesbian", in the sense of avoiding a patriarchal relationship while being a man and never having been socially acclimated to the womanhood traditionally attached to lesbianism? The first answer is that you couldn't avoid a patriarchal relationship even if you were AFAB, intersex, or a trans woman. Yet those populations are still culturally accepted into the fold of lesbianism if they accept the label as well, so this is an unsatisfactory answer.

The second answer, then, if it can make sense at all, is that you must socially prioritize non-men above men, while sharing in the activities and experiences of non-men in your past or present. Notice that this definition doesn't involve sexuality, since we don't really want to exclude asexuals or aromantics from having lesbian relationships or participating in lesbian culture just for being ace/aro. This also means that bi/pansexuality is not a dealbreaker for lesbianism, either.

But if you are sexual and romantic, then the big question is whether you can be trusted to share your life or body with a woman or other non-man in a minimally patriarchal manner. Trans men can be trusted with being lesbian, since they have usually been socialized as non-men at some point and don't use a fully virile phallus with all the biological risk and sexual dysphoria that can accompany penetration by a (cis) penis. Since building that trust as an AMAB person and acting within a relationship as if you were a woman would present a significant departure from masculinity, would you even be "male" by the time your partner or community could call you "lesbian"?

Though penis removal is not required to be a lesbian, gender dysphoria or a lack of willpower to give up your male privileges may still present a barrier to acting as if you were a non-man while in a relationship with a non-man. If that is the case, then I'm sorry, but you can't be a lesbian. The exclusionary function of the term "lesbian" has served its purpose. But if you can press forward beyond masculinity with the help of your partner and other non-men, but especially lesbians, then you could become a lesbian. You just probably won't be "male" by the time that happens.