As a former femboy, I think the bigger problem than "do femboys hate trannies" is that it's just not as easy a lifestyle to sustain as being a tranny. There are lots of ugly trannies, but no ugly femboys, primarily because the standards for being considered one have gotten aggressively high lately. I was never a model but I'm slim and look cute in leggings, so that's really all you need. Or at least, it used to be that way.
Unfortunately, a lot of femboys now are one of two things: Pre-HRT trannies, or (i kid you not) literal women masquerading as the opposite gender for clout. That makes it incredibly difficult to stand out.
I also really, really despise the term "twinkdeath" and the damage it's caused to the femboy community. Trannies weaponized natural things like getting wrinkles and thinning hair to make it seem like femboys can't exist after a certain point. Ignore the entire glam trend from the 80s, ignore that we're actually making progress in de-aging solutions, let's just shame any man who is proud he can preserve his boyish features because we're psychopaths and we can get away with it.
So not only did trannies tarnsh the good name of femboys and then attack them for persisting, not only did confused women and grifting trannies dilute the term itself, you now also have to contend with the fact that it has never been less attractive for a guy to be effete in the normie view. It's just stigma on top of stigma, hence why most femboys just hide indoors all day and stop caring. Society stopped rewarding cuteness and is misandrist to a core, even when it doesn't make sense.