Tomboy is still fine to use, but it's a term typically directed towards cisgender girls who have interests and hobbies which are typically regarded as masculine or intended for boys, i.e. sports, cars, video games, etc. I'm not sure I would advise conflating it with gender identity, however, as it's a term that many people still use and self-identify with, so it might lead to confusion. Namely, I think it's wrong to regard your interests, fashion choices, and etc. as directly linked to your sexual orientation or gender identity. They are at best secondary characteristics that often correlate to, but are not the direct result of, both of those things. Someone can have interests that are typically seen as masculine, or dress entirely in clothing marketed towards men, or have the most muscular physique and still consider themselves a woman. Just as there are men who have traditionally feminine interests but still identify as male.
It's worth a note that it hasn't always been like this; it's taken centuries for girls to be allowed to enter typically male-dominated areas and not be scoffed at or socially ostracized. And there are many areas where they still are. Women who are into body building or more physical contact sports (football, wrestling, etc.) are given much more scrutiny than other activities that are deemed acceptable for girls. And it is still difficult to go into an electronics store and not be faced with a sales rep trying to get you to buy something you don't need because they think you're too stupid to know better (which isn't a problem that women exclusively face, but the way it manifests is tangibly different), or have patronizing customers who will use your gender as a springboard to over-analyze every purchasing decision you make. And that's just the more petty trifles that are annoying but not necessarily harmful. Depending on where you're from and what social circles you're surrounded by, girls may still face aggression or are treated as aliens for expressing interest in things outside traditionally feminine activities.
The reason boys tend to receive a lot more noticeable aggression (aside from the obvious societal prejudices that are much heavier and I won't go into here) when they engage with more traditionally feminine aesthetics and activities is because social progress has shifted the conversation away from "girls should focus on being more ladylike housekeepers" to "well, it makes sense that women would like to have the same rights as men, because men are awesome and everyone wants to be a man!" The implication being that no one would willingly choose to be a woman.
It's why I feel questions like "Why aren't there more female engineers?" are often sidestepping the more important question of "Why are female-dominated career fields, such as teaching and nursing, seen as 'lesser' options?" Because even in discussions of sexual equality, men are still erroneously used as the ultimate litmus test.
