2,503 dead people were registered to vote in Detroit and the city was sued for the same in 2019. This incident is not related to the 2020 elections.
Incidentally, the Public Interest Legal Foundation had filed a lawsuit in Federal court in 2019 against the city of Detroit, alleging irregularities in the city’s voter file, which claimed the discovery of 4,788 duplicate voters registrations, 32,519 more registered voters than eligible voters, 2,503 dead people registered to vote. However, the lawsuit was dropped in July this year after the city made inroads into fixing the issues raised by the non-profit group. Detroit Clerk Janice Winfrey said her office did look into a few specific claims made in the lawsuit and the conclusion was that it was a typographical error.
This incident is in no way related to the 2020 presidential election in the United States and thus, this claim can be regarded as baseless.