If there were evidence that members of the Biden campaign had "colluded" with China, would Republicans be claiming Biden had "colluded" with China? I think we both know the answer to that -- of course they would.
What we know -- members of the Trump campaign did work with Russians with ties to the Russian government. That isn't in question, it is in the Mueller Report as well as the Senate Intelligence Commitee report. We know one of Trump's campaign managers was sharing Trump campaign data (polling results) with a Russian.
It is true, there has been no evidence that ties the President to the actions by his campaign. The closest is Roger Stone, who not only worked with Wikileaks and possibly Russia in the release of the DNC hacked information, to coordinate those releases with the Trump campaign.
Additionally, it is alleged that he participated in a "cover up," about 10 different claims, to prevent the Mueller team from fully finding out the extent of cooperation between the Trump campaign and Russia.
For this reason, "Russian collusion" is not really a good "whataboutism" to use. The FBI, as has been found by every investigation, had ample reason to investigate. It was the actions of Trump appointees, including Flynn and Sessions not being forthright (in Flynn's case actual lies) that largely made it politically necessary for the Special Prosecutor. And, again, even a Republican led Senate investigation found there were serious security risks and implications involved with the ties between the campain and the Russians.