Looking at the South (using percentages of the population):
English ancestry
1980 26%
2000 8.4%
2021 10.2%
American ancestry
1980 9%
2000 11.2%
2021 7.5% (6.5% single ancestry)
German ancestry
1980 14.2%
2000 10%
2021 9.1%
Irish ancestry
1980 16.8%
2000 10.7%
2021 9.1%
Not reported
1980 13.7%
2000 n/a
2021 22.1%
The South was clearly the most English-reporting region in 1980, but the drop in English ancestry responses was more pronounced than in the rest of the country. Odd to see it fall behind German and Irish in 2000.
Yeah this is a great example of how underreported English ancestry really is. There is just no possibke way based on immigration history and moving patterns that the south could have more Germans or Irish than English.