A case would have to be presented to the court. Assuming the court decides to hear it, their decision would be legally binding. But that only applies to that case. There couldn’t and wouldn’t be a case of “who won the election”, it’s decided by the states and is clearly indicated in the Constitution. That’s why Trump desperately wanted to “send it back to the states”. The state legislatures and governors would be able to muck with the results, but thankfully that didn’t happen.

The most important votes are for local officials and don’t forget it.