When it’s a SINGLE PERSON IN THE RACE, no.
They didn’t say all trolls can’t read. They said a single character can’t, as it was a character flaw they decided to use as a storytelling reason to help show Lor’themar communicating with the other races, since he’s only really been seen with other elves.
Again, read my post. If it was “All trolls can’t read” or even “The majority can’t read” - yes, it’d be racist.
But it was ONE SINGLE CHARACTER. Characters are allowed flaws, yes, even flaws that are stereotypes, as long as that’s not their only quality. Which it isn’t for Zekhan.