There really isn’t. The “punchline” here is predicated on the idea that the reader will assume the character will react with transphobia, as if transphobia is the default reaction, but if you don’t assume that reaction either because that’s not your worldview or you’re familiar enough with the creator to understand the context of their work, then there is nothing left to serve as a punchline. I won’t say “virtue signaling” because that’s a stupid phrase and frankly there is legitimately some value to the signaling of virtue in the first place anyway (especially when said signal is one of welcoming to a disenfranchised community like our trans brothers and sisters), but the only “joke” here is pandering. It’s “hey you expected me to be awful but I’m actually incredible!!,” and that’s not a punchline.