So this is a really complicated question with a very complicated history. I can only speak for myself and others with my same experience, and you should absolutely speak to other transmasc lesbians because they will have other reasons than this. I first want to give you a quote from the book "Butch Is A Noun," By S Bear Bergman. This is by far my favorite book dealing with gender, and quite possibly my favorite book of all time, and it is something I would highly suggest you read if this is a topic that you want to learn more about. This is from hir essay "I Know What Butch Is," and lays the groundwork for just about everything I'm going to say.
"I know what butch is. Butches are not beginner FTMs, except that sometimes they are, but it’s not a continuum except when it is. Butch is not a trans identity unless the butch in questions says it is, in which case it is, unless the tranny in question says it isn’t, in which case it’s not. There is no such thing as butch flight, no matter what the femmes or elders say, unless saying that invalidates the opinions of femmes in a sexist fashion or the opinions of elders in an ageist fashion. Or if they’re right. But they are not, because butch and transgender are the same thing with different names, except that butch is not a trans identity, unless it is; see above.
Butches are always tops. They always fuck the girls, and, for that matter, their partners are always girls; there is no such thing as a butch who is attracted to men. Well, transmen, but that’s just butch-on-butch repackaged as faggotry. But no non-trans-men. Unless the butch in question is a non-trans-man, then it’s okay. Except that non-trans-men cannot be butches, because butch is a queering of gender that assigned-male people cannot embody, unless they occasionally can, in which case they have to be gay men. Or the partners of femmes. Or not. But no one with an assigned- female body can be a butch and do it with assigned-male men. Unless they’re femmes. Or butches. I’m really putting my foot down on this one."
I hope that's clear and concise!
In all seriousness, though, this passage is so integral to understanding lesbians who are also trans men. For as long as butches have existed, there have been transmasc butches - some binary, some not - and transbutch individuals (like myself) that may or may not consider themselves transmasc. Butchness is so intrinsically tied to queer masculinity that expecting there to be a clean cut line between trans men and butches is ludicrous. There really is not that big of a difference between a straight binary trans man and a cis butch lesbian, in the eyes of society and in their legal needs, so when you get into the weeds of trans butches (of ANY flavor), things get even more messy.
Now, not all butches consider themselves lesbians, and not all transmasc lesbians consider themselves butches, for all manner of reasons, but we are siblings in arms. Most transmasc lesbians I know grew up as lesbians, in lesbian community spaces, fighting for lesbian rights. Many of them were butches, and some of them still identify as butch in conjunction with their trans identity. When you grow up with something as a formative part of who you are, the relationships you have, and the network you rely on, changing your gender identity does not mean that you have changed how those formative things built you into yourself. Me changing my gender does not mean that my previous relationships are void, or my network no longer wants me, contrary to what the popularization of lesbian separatism and radfem rhetoric might have you believe. I am transmasc, and I am in a women's chorus. I fight for feminist causes, and go to pride flying my butch flag. All of these things have not changed with my transition, because they are a part of me.
This belief that there are hard and fast lines between identities is not a widespread one outside of the internet. I have old queer friends in their 60s whom I'm unsure are trans or queens (or both!), and it's not really relevant when we're hanging out. I have old butch ladies in my chorus that are the only people I don't mind calling me "she", and I know a gay man who is deeply in love with his wife. Queerness is a vibrant spectrum, and the people who have told you otherwise are doing a disservice to you and to every queer person on the planet. It's messy, and wild, and the chaos is what makes it so alive. It's how you end up with people like me - a bigender transbutch lesbian, in a poly relationship with one cis man I've been with for nine and a half years (long before I even knew I was trans) and one nonbinary man I've been with for five (hello @doki-deku !). I'm a fucking mess of identity and labels because my labels are there to serve me, not anyone else. They are tools to communicate who and what I am to others. There is no word for what exactly I am other than queer, and I love that! It's why the word is so important to me! But when I'm talking about my space in the lesbian community, I am going to use the word lesbian because I am one. What other people have to say about that is none of my business.
I really hope you do talk to other people about this, and please please please read Butch Is A Noun. The book is spectacular, and is much more eloquent than anything I could write on the subject. Bear is a phenomenal writer and educator, and you'll love hir book. Hope this was a good step into the soup, and I hope you have a lovely day.