No, Barr was not part of a secret plot against President Trump.
https://www.nytimes.com/2020/12/02/technology/no-barr-was-not-part-of-a-secret-plot-against-president-trump.html
After the attorney general said the Justice Department had not found voter fraud, pro-Trump personalities accused Mr. Barr of being part of a nefarious scheme against the president.