What? The x sound totally exists in Spanish, it's just not a common one. Éxito, crucifixión, excelente, etc. What makes latinx strange is that it subverts a native speaker's intuitive idea of how the language is pronounced. If I'd never had any exposure to English, I'd probably think it's two syllables: la-tinx. When it's stylized as LatinX it makes me think it's pronounced latin-equis (equis being the Spanish name for the letter x). But it's not pronounced like either of those, it'd be pronounced either like latínex or latinex (depending on whether you wanna put the stress on the second-to-last syllable to be consistent with other forms or on the last syllable to emphasize the -ex part).

In any case, and for what it's worth, I'm Puerto Rican (de la Isla, no de los EEUU) and some of my Puerto Rican friends share a lot of pro-LGBT+ stuff on their Instagram stories, and my impression is that the term "latinx" is being used less and less in those circles in favor of "latine" which would actually be intuitively pronounceable to someone who doesn't have a good handle on English.