I thought that the presidential vote by the people was the only constitutionally mandated one?
Nope, Article 2 says the President is chosen by the electors, who are appointed in whatever manner the state legislature decides.
Article 1 mandates that congressional representatives must be elected by the people, so maybe that is what you are thinking of.
The “presidential” vote is a vote for ELECTORS not a person.
Presidents are elected by these ELECTORS who have committed themselves to vote for a particular candidate but are not legally bound to do so.
Electors have the entire power over a presidential appointment.
REPUBLICAN principles are what are guaranteed within the constitution, not democratic principles.
So we elect state legislatures to represent us which then elects electors who then elect a president.
We are a representative republic. In short, the winner of the popular vote only gets a participation trophy.