Of coarse, being a Femboy is 100% valid. I know what the post is implying and I'm acknowledging people who identify as male being GNC and liking cute stuff are still valid as their identity, despite some people suggesting otherwise (not saying you're doing it by the way). I know that egg culture is very much a problem for GNC people and I'd just like to say, give it a rest, don't they go through enough already, be supportive of them, that means respecting their identity, even if it contradicts your idea of gender stereotypes i.e. a boy who chooses to dress and act cute and feminine but still identifies as male. The important part is how they identify, not how they present.
Oh and I know that people are going to say "But FirstMajesticComet, there's a line between being a Femboy and being transfem" I would say yes, yes there is, and it's determined by how they identify, gender identity is self-deterministic, it's not an outside factor, it's true because the person says it is. Fighting or arguing against it is invalidating and disrespectful to their identity, keep that in mind.
Here's a chart showing presentation and how they identify, notice that presentation does not affect or determine identity in this:
I apologize if my comment seemed harsh and cold towards the OP specifically, I have no ill intentions towards them as a person, or even their actions here. I only seek to show how it is important to recognize and respect the identities of GNC people and not crush or invalidate them inadvertently (or intentionally if you think they're "in-denial", it's still invalidating them because you're not respecting who they say they are) they do not deserve this kind of treatment. Remember the golden rule, treat others the way you want to be treated.