Right now Republicans are worried about getting Trumps election victory certified. Not because Dems are going to try and block it, file frivolous lawsuits or stage an insurrection, but because REPUBLICANS, are trying to oust Mike Johnson as speaker and if they do it could throw a monkey wrench in the whole process.
Harris as leader of the senate is in charge, but the first move of the new Congress, since 1789, has been to elect a new Speaker. They do that on Jan 3, and nobody knows if the GOP has anybody who can get the votes to be speaker yet. It's not at all Certain Johnson can.
And there's talk the Dems are just going to play along and say Harris will be happy to certify Trump, as soon as the other required stuff is done, including the speaker of the house.