I've had it go back and forth my while life (at least that I can remember). I'm my youth, I mostly was male in my dreams, but had the occasional dream where I was a woman (and some dreams that really should have cracked my egg sooner). I realized I was trans about 9 months ago. By "realized", I mean that I had been thinking about it seriously for 2 and a half years (and had fleeting thoughts long before that), and 9 months ago is when I was finally confident that it was who I am. Since then, I have dreamt of myself as a woman much more often. I'm on hormones, and I don't dream most nights (always been like that), but its rare for me to have a dream where I'm a man nowadays, despite the fact that I haven't outwardly transitioned (only among friends and online am I presenting fem because of some life reasons that make it unsafe right now). I spend most of my time alone in my room, and I present fem to myself in the way I behave, in my mannerisms and such. I have spent a lot of time changing my voice, so when I'm alone, I speak to myself in my new voice, even though I never use it with anyone else in person. I've very significantly changed the way that I think about myself, and for me, that has affected my dreams significantly. That's not to say that just because someone else has a different dream experience that they way they think of themselves is differently than I do. Dreams are a really mysterious thing, and everyone has different experiences with them. They aren't necessarily representative of your real life, or your real beliefs or thoughts, though they can often be influenced by them.

But I think something that has actually had a significant effect on my dreams is how much I've been daydreaming since my realization. In daydreams, I'm entirely in control, and I imagine myself as the girl I want to be. I think that has affected my dreams significantly, and it's definitely influenced my conscious thoughts. I don't know if it's related, but now that I've gotten used to my voice, my inner monologue has changed. I've almost outed myself by accidentally using the "wrong" voice before because of it, but I really think that it's a lot of little things that have caused my thoughts and dreams to change.

I think it's going to be different for everyone. Just remember that your brain loves to use the same connections that it has used your entire life. It loves being lazy and ignoring new things when it can get away with it. Your brain controls your dreams, despite it not being conscious control, so it's likely to use connections from the before times when you are dreaming. That doesn't change who you are, and it doesn't make you any less (or any more) valid. That's just the brain doing it's thing; falling into patterns established when it was younger because it likes to be lazy about it.