SCOTUS cannot order new elections - there’s no provision for it in the Constitution for ANYONE to have such a thing.
What it CAN do is to reverse or prevent a traditional certification of the “win” by Biden. That then allows the following Constitutional remedies to occur:
1) The PA legislature can decide (as it explicitly is empowered to do under the Constitution) who, exactly, are hte Electors for their state; or
2) If the legislature either cannot or will not decide this issue, then either PA loses its EVs for this election OR, if no candidate wins 270 EVs, then the House of Representatives shall vote on who is the next President (one vote per state delegation).
Those are proper remedies. The Court traditionally doesn’t want to rule on political issues, and when it rules on ANY issue, it usually says something to the effect of, “You cannot do this, now we direct the lower court to rule in this case with that ruling in mind.” IOW, they almost always fall back on having some other body actually make the decision that it is empowered under law to make - they just clarify what the law actual states.
For better or worse, we have gotten used to unconstitutional remedies ordered by the Courts. (Consider the Boston School Busing Order.)
ML/NJ