The line was made up by the rightwing.
"Vice President Kamala Harris might soon get a new official title: 2024 Democratic presidential nominee. In the meantime, Republicans have revived a title they gave her in 2021: “border czar.”
Claims that President Joe Biden named Harris the “border czar” and that she is responsible for overseeing U.S. border enforcement gained prominence at the Republican National Convention as the party sought to link her to his immigration policy.
The refrain intensified once Biden dropped out of the race and endorsed Harris. It was echoed in ads and by Trump campaign surrogates, including Ohio Sen. JD Vance, the Republican vice presidential nominee."
https://19thnews.org/2024/08/border-czar-kamala-harris-immigration-fact-check/