The case is moot. If the Democrats has been able to show that Trump was on the payroll of a foreign government, that would have been an impeachable offense. If the Democrats showed Trump was simply running a business, the Democrats would look silly since it is clear that presidents are allowed to moonlight (and many of the early presidents spent much time on their business interests including selling things to foreigners).
Of course, if you believe, as Trump does, that Trump really won the election, the case wouldn’t be moot since Trump is still president. The Supreme Court clearly feels otherwise.