1991:
The "xenophobic Emperor" was a thing made up by the fans, many of which now run OutrageTube channels where they scream about women and POC ruining Star Wars.
Canon....
…I have no issues with aliens myself—some of my best friends are nonhumans—but some grav-ball fans object to alien physiognomies, seeing them as giving nonhumans an edge.Janus Fhurek's xenophobic rationale for kicking Frid Kelio and Hench Sina off the AppSci SaberCats Xenophobia, also known as...
starwars.fandom.com
"By the time of the Battle of Endor, it was widely known that the Empire pursued a xenophobic policy that favored humans and treated aliens as subjects or threats.[5]"
Aftermath: Life Debt
"The Galactic Empire was known to favor humans while looking down on non-humans or "aliens".[9] As a result, the Empire's government and
military was largely dominated by humans, and it was rare to find nonhumans serving as
Imperial officers.
[10]"
Star Wars Rebels: The Visual Guide
"The Imperial Academies were dominated by humans, and aliens like Thrawn found themselves having to navigate racial prejudice and outright hostility.[6]"
Thrawn
"The Empire implemented the "High Human" culture prevalently on Coruscant, their capital world, suggesting the superiority of the human race.[13]"
Star Wars: The Rise of Skywalker: The Visual Dictionary
Lunarorbit
correct.