Anh from BeautyBox is not the first Vietnamese k-pop idol.
If you want to get specific here, they debuted on September 23, 2021. Lalary, a co-ed group (Eddie Valencia, my dudes. Iconic man right there) debuted two years earlier on August 29, 2019, with Vietnamese member Hope. And then, continuing more than that, both Z-girls and Z-boys, with respective debut dates of February 23, 2019, and February 22, 2019, have Vietnamese members Queen and Roy. And then, going all the way back to 2014, A-Daily debuted on December 3, 2014, with member Jade, who left the group in 2015. So no, Anh is not the first one.