Gender is a complex multi-faceted expression of many factors not fully captured by a binary "Female" or "Male". Further, gender, especially in western society, carries a legacy of cultural norms and mores often at odds with reality. But by exploring how our expression of gender invokes feelings of dysphoria or euphoria, we can better understand our true gender identities.
It is still a gross simplification, but suppose we project what we call gender to a single dimension from Masculine (on the left, say) to Feminine (on the right). On the far left is ultra masculine, to use western stereotypes: loving sports, excessive drinking, body hair, giving strong handshakes, etc. As we move to the right, these behaviors moderate and become more feminine (again, to use stereotypes: wearing dresses, being more emotionally supportive, being a mom, speaking with a higher pitch, etc). Your specific cultural experience may align differently, so consider what expressions might simplify gender into a spectrum.
<-Very Masc----Masc----Non Binary----Fem----Very Fem->
Where you might be on this axis? Do you present mostly female, but not entirely? Do behaviors/traits associated with other parts of the spectrum make you uncomfortable? For example, maybe you are a woman but have some amount of body hair. Whenever you notice it, you experience dysphoria (by which we mean gender-specific sources of stress, or joy for euphoria) from something that is associated with being masculine. Or maybe there was a time you were forced to wear a dress, something more feminine than you prefer.
At different places on the gender identity spectrum, you may experience different levels of dysphoria or euphoria. Perhaps if you identify as female, your Gender Expression curve looks like this:
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Just to give some examples, if you're non-binary, maybe your point of maximum euphoria shifts left (again, this is a simplification!).
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Of course, gender identity can be more complex than this. Perhaps you are somewhat comfortable with both male and female traits, but the space in between is uncomfortable. This is a form of bigender:
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Even in this situation, one might still have more euphoria in one place on the gender spectrum. Perhaps you are bigender with a female preference:
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Of course, you may have multiple prefences (i.e. local maxima). Maybe you're multi-gender with a gender expression curve like this:
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There are many possible gender identities; these are just a few examples to demonstrate the utility of the gender expression curve. If your identity isn't listed, see if you can sketch what the curve may look like!
One identity this curve fails to capture is genderfluid. In that situation, you may have a particular gender expression curve, but it changes in time. One week it could be masculine preferring, and the next it could be bigender with feminine preference.
Further, these kind of diagrams combine many internal and external factors. The society you live in may make life difficult for certain gender expressions (e.g. making women second-class citizens, ignoring the existence of non-binary identities, etc). But, it's still important to understand what your internal curve is, so if necessary, you can change yourself or your environment as needed.
So far, we've only talked about what euphoria you would experience with different gender expression. But what if you are living at one place on the spectrum (due to cultural norms, medical situations, or whatever), but you'd have a more euphoria at another place?
For example, perhaps you were AFAB, but you know you have a masculine gender-identity. You may be dysphoric by having to live as a woman (perhaps you cannot safely transition nor socially present as male).
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A similar situation can arise for bi/multi-gender individuals. Again, consider if you're AMAB and bigender with a female preference. Maybe you've been living as a man (because you hadn't figured out your gender identity, say), but realized what your gender expression curve actually is. Sure, you could continue presenting male; it wouldn't be as miserable as for the above trans man forced to present female. But you're not living life to its fullest; and you'd be living with a constant dysphoria just from existing. If you can transition to a more feminine state, you may realize lower stress, more happiness, and more fulfillment.
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This is similar to the question of "How do I determine if I am trans?" Most cis-gendered people are comfortable in their assigned gender, so even asking the question suggests you may not be living at your global maximum for gender euphoria.
There is not yet a standardized set of experiments/questions to determine your curve (online quiz in the works!). But you can run your own experiments, be they mental exercises (e.g. "What if I wore a bra?"/"What if had a beard?") or physical tests (e.g. wearing a dress, using different pronouns, etc).
As you do so, consider where each test would put you on the gender spectrum, and how much dys/eu-phoria you feel from it. Start plotting these points. Over time, you will see approximately where your curve lies as you explore the gender expression space.
Recommended Resource: You And Your Gender Identity by Dara Hoffman-Fox