” Review the forms filled by people from the area who immigrated to the US in the early 1920s. There was no such thing as Ukrainian at the time.”
I presume you have never researched this yourself and are simply regurgitating some propaganda you mindlessly swallowed.
US Census 1920 language data: https://www2.census.gov/prod2/decennial/documents/16440598v2ch08.pdf
A whole lot of people identifying as Ukrainian/Ruthenian speakers
For the Don Cossacks, they were their own ethnic group, but they spoke a dialect closer to Ukrainian than Russian.
Sorry, typo on my part, make it 1900. Don Cossacks isn’t an ethnicity, they don’t have any specific dialect. Ukrainian itself is essentially a dialect of Southern Russian with some Polonisms included.