I've heard this argument but I presume the PA legislature has already decided how the state picks its electors and written it into law.
The PA constitution also probably dictates how that law can be amended/changed.
It seems to me that a unilateral move by the legislature to change existing law would run afoul of the state constitution, and I imagine the USSC would uphold that aspect of it.
Now if the legislature had never written any laws about choosing electors they may very well have the right under the US Constitution to act unilaterally.
“I’ve heard this argument but I presume the PA legislature has already decided how the state picks its electors and written it into law.
The PA constitution also probably dictates how that law can be amended/changed.”
A quick search shows that there is a law currently in place, but that the state constitution is silent on the matter. I also think the Supremacy Clause and a strict reading of the Constitution would come into play, in that a state law or statute cannot override the Federal Constitution by adding any prohibitions to the Legislature’s ability to award the electors as they see fit. Remember, the ones who would decide this would be Thomas, Alito, Gorsuch, Kavanaugh and Barrett - Roberts would not be a factor.