The "I'm ___ and don't personally know someone" option is a little weird to me, and probably better expressed as "I'm ___ and and don't know any trans people that are out to me".
I'm nb and trans. I have known a handful of coworkers, many close friends(including one person that I've been close to since we were both cis-identified) and one family member that are out to me as trans. This isn't to mention the many trans people I know through support groups.
I personally am privileged to be recognized as cis by the general public and I don't disclose being trans to coworkers or acquaintances. I've had to awkwardly out myself to a cop who kept calling in a check on a "white female". I've run into confusion at hospitals with workers that just couldn't process that I wasn't cis unless my pants were down, and that didn't trust my male-labeled ID. The sexual harassment I've fallen victim would have likely been much worse if my attackers had realized I was trans.
I have had zero surgeries, permanent procedures(HRT aside, but including any sort of facial hair removal) or change to my legal name/gender markers. I know a ton of trans people with more passing privilege than I have, that basically won't disclose to anyone that they're trans. And this is just describing the binary trans people that have transitioned, there are so many other trans, nb, agender, and gender nonconforming individuals that are invisible for other reasons.
I'm not opposed to the idea of the thread, and don't suspect any ill intention from the OP or any cis people here, but the unspoken bias that cis people have about knowing if someone is trans or not is still really pervasive, and not indicative of reality.