If the “B” in LGBT stands for “Bisexual”, doesn’t that mean that there are only two genders?
Except, not quite.
The term “bisexual” was coined in the early 1800s, but was first used with the contemporary meaning in 1914. Since the 1950s, its use has ballooned in popularity and mainstream recognition. A product of its time, this 104 year old term reflected the outdated view that only two genders existed, hence the use of the prefix bi.
Omnisexual (dating back to 1959) or pansexual (dating back to 1917, albeit with a different meaning) are both terms that refer to people who are attracted to people of any gender. The latter, pansexual, is used much more commonly.
I’m very happy to debunk this nonsense, but I recognize it’s a fruitless endeavor. The people who make these sort of “jokes” are not typically good faith actors; they’re just cringy trolls who seek to “TROLL THE LIBS!” instead of keeping up to date with modern science.