Until maybe two years ago, I hadn’t heard of it either (I live in the UK). It seems that it has mostly been a problem in the US, where the term “Anglo Saxon” came to gain white supremacist meanings, along with nationalism and racial purity, etc. Abhorrent, of course. But in the UK (and I suppose parts of Europe?) “Anglo Saxon” broadly refers to the time period between the end of the Roman period and the beginning of the Viking Age, and doesn’t have the same horrible meaning that it does in the US. It was news to me when I first heard about that, but I’ve since read more. In her recent book Buried, Dr. Alice Roberts has a whole postscript section about the use of the term and how its meaning has changed over time across the world.