I don't think there is any set constitutional method for how the the individual state's determine electors. I also think having a popular vote and assigning electors according to that vote is a formality.
Basically, people voted for a state legislature which then voted for a President via electors. Similar to how Senators were chosen, except in the Senator case there were no electors necessary because the vote was immediate. Presidential electors were sent to DC to vote later.
What you have, here, then, is a muddying of the waters scenario by the dems/GOPe, gaslighting to populace to think there is only one legal way to choose electors., and/or that only one set of electors per state is possible. The end game is to convince the populace that Trump broke some Constitutional guideline to maintain power, and that would be considered an insurrection.
The dems/GOPe can stop Trump from ever becoming President again by convicting him of insurrectional behavior. Arresting him for any other crime won't matter. So, end game is to convict Trump for leading an insurrection. Always start there and then work back to figure out the current game the dems/GOPe are playing trying to accomplish that.
Trump must have had high ranking Constitutional gurus telling him what to do. He's probably legit and the dems/GOPe will walk into a trap.