The Anglo-Saxons were a people made out of immigrants from Germanic Europe that migrated to what is now England and mingled with indigenous British groups, tracing back to the 5th century. It's often used to refer to the language spoken in England and eastern Scotland until the mid-12th century, also called Old English. The culture and language were pretty much defunct after the Norman Conquest.
Something I found out / realized not that long ago: the Norman Conquest wasn't actually vikings, but French from Normandy. Mind you, vikings from Denmark and Norway were also a thing around the same time.
They were a mixed people, partly descended from Vikings. Not only people descended from Vikings invaded England. You had non Viking French in there too.
The influence of Anglo-Saxon culture is the main reason why English culture isn't the same as French culture, so I don't think you can really say it's defunct. The influence of French is stronger in southern 'BBC' English, but England has a lot of regional dialects that still retain a lot of quite ancient linguistic influences.
https://en.wikipedia.org/wiki/White_Anglo-Saxon_Protestants#...
The only remaining usage of Anglo Saxon in the contemporary USA is as part of the already antiquated “WASP” term.
Anglo Saxon in reference to the US is in my very-online anecdotal experience roughly ~70% French speakers, 15% continental Europeans, and 15% race based nationalists.
Americans usually just say “white”, even when specifically referring to classic WASP cases, especially after the Germans, Italians, and other ethnic groups were absorbed over the last century.
In Germany the term is used to refer to the germanic tribe of the same name, which settled in Britain, and its asserted descendents, i.e. a somewhat loose collection of Great Britain, the US, Canada, Australia and New Zealand.