At first glance, this is pretty devastating news for Trump's chances. The PA case was, as far as I know, the best shot because the court had previously opined on the issue and even issued orders to segregate ballots. But it appears they are not interested in getting involved, even to the minimal extent necessary to decertify an election and ask the state legislature to decide.
It's hard not to take that as the Supreme Court signaling that it's not interested in this issue at all. However, the denial was for a request for emergency injunctive relief. It is possible that a normal appeal will be filed, on a normal schedule, and the Supreme Court may take that. However, that seems like a bad bet given how they disposed of this case.