On December 1, the Trump campaign filed a lawsuit directly with the Wisconsin Supreme Court, asking that hundreds of thousands of votes be excluded from the official count. See this story. The lawsuit does not allege any fraudulent activity, but says that many votes were cast in a way that violates state law.
https://www.detroitnews.com/story/news/politics/2020/12/01/trump-files-lawsuit-challenging-wisconsin-election-results/6477770002/
AP story