Double jeopardy means nothing to the “Just Us” Department.
Multiple criminal charges in separate jurisdictions arising from the same incident. That’s not “double jeopardy”.
In fairness, the legal doctrine of ‘separate sovereign’ is more than 170-years old. The state is sovereign as is the federal government.
You can kidnap a person in one state, drag them to another state and be in criminal peril in both states and federally, all for essentially the same crime.
I don’t think the federal prosecution of Chauvin makes any sense or is justified. But, that doesn’t mean it’s ‘double jeopardy.’