Which...they didn’t do. Republicans blocked having witnesses or documents appear during the Senate impeachment proceedings.
So no, collusion was not largely proven to be false, because once it moved to the Senate, nobody was called to testify under oath since Republicans blocked it. The Mueller report remains largely unvetted, and while its conclusions are weak due to Justice Department policy on what a sitting president can be charged with (or accused of? I am not clear on this distinction), its evidence appears to be strong. We don’t know if it holds up or not. It was never rigorously examined, because Republicans blocked it.