What would happen in this scenario?

[Shaula🏳️‍⚧️]

Trump doesn't concede to Biden but still leaves the White House before inauguration. Biden handles the coronavirus better than Trump but another wave still hits in February 2021. The economy slowly recovers over the next couple years, slower than economists predicted, partly due to a Republican senate obstructing almost every law Biden tries to pass. Trump buys OANN and turns it into his own network, while he still claims to be the true president, running a sort-of shadow presidency ou of Florida (absolutely pointless but still holding rallies and press conferences and the such, essentially LARPing).
In 2022 the Senate stays about the same, a slight Republican majority while the House narrowly flips non-Atlas red. Biden announces he will not run for a second term, opening the way for the democratic primaries, with Harris way ahead of Ro Khanna, Elizabeth Warren (who drops out before the first primary) and a surprisingly successful Andrew Yang. After winning a close primary against Yang, Harris picks Sherrod Brown as VP.
Meanwhile in the Republican primaries, Donald Trump runs again, announcing as early as May 2021. Most "Trumpist" Republicans don't run, supporting Trump's candidacy to "give him back his stolen term". Trump crushes his competition, Nikki Haley, Mitt Romney and Alex Jones (who's candidacy becomes a massive meme). Trump wins every state except South Carolina and Utah, clearly having the support of the Republican voters, although many establishment people are not happy.
Trump picks Pence again as VP, mostly to create a form of continuation from his first term.

Who wins? Trump or Harris?

[Tekken_Guy]

Harris, easily. Trump will be a has-been by then, and will not have the soft support he did when he was president. Also, demographic changes will go against him.