Mueller didn't debunk anything russia related -
https://www.lawfareblog.com/new-russia-sanctions-resolve-mystery-mueller-left-unanswered
The next piece of information about Kilimnik’s role arrived in the Senate Intelligence Committee’s mammoth bipartisan summer 2020 report on Russian election interference. The Senate report is far blunter than Mueller on the subject of Kilimnik’s connections to Russian intelligence, writing directly that “Kilimnik is a Russian intelligence officer.” And it suggests that Manafort knew, too: “Manafort … at some point harbored suspicions that Kilimnik had ties to intelligence services. Manafort was undeniably aware—often from first-hand experience—of suspicious aspects of Kilimnik’s behavior and network. Nevertheless, Manafort later asserted to [Mueller’s team] that Kilimnik was not a spy.”
The Senate report provides a little more information about what the mysterious polling data might have contained. According to two Trump campaign associates, Manafort seems to have shared data with Kilimnik on “polls that identified voter bases in blue-collar, democratic-leaning states”—including Michigan, Wisconsin, Pennsylvania, and Minnesota—“which Trump could swing,” along with data on negative public sentiment toward Trump’s 2016 rival, Hillary Clinton.