It's odd that the President would out-perform his 2016 numbers and then be beaten by Joe Biden even though the President doubled his cut of the black vote, on which the Democratic Party often relies. It's even stranger, though, that Joe Biden's titanic landslide didn't come with coat-tails: the Republican Party kept the Senate, and added to the House.
One explanation for why that might happen is if Republican voters turned on Trump, but otherwise continued to vote for Republicans down ballot. If that were true, you'd expect to see lots of races with Republican Senate numbers well in advance of the President's numbers. But the results don't show that.
What the results appear to show is that Trump and the Republican Senators running alongside him mostly posted similar numbers, as you'd expect if Trump voters were also likely to be Republican voters down-ballot. Biden's numbers are the ones that look weird. In swing states Biden votes are not tethered to the Senate numbers.
Michigan
Trump: 2,637,173
GOP Sen: 2,630,042
Dif: 7,131
Biden: 2,787,544
Dem Sen: 2,718,451
Dif: 69,093
Georgia
Trump: 2,432,799
GOP Sen: 2,433,617
Dif: 818
Biden: 2,414,651
Dem Sen: 2,318,850
Dif: 95,801
So one possibility is that somebody's inventing Biden votes on a tight schedule. In Georgia, they knew after Tuesday night counting got halted that they needed around 100,000 votes. Since each one takes time to process, time is limited, and you can't expand your personnel much without running risks of being discovered, they're turning out the Biden votes without bothering to fill out the rest of the ballot.
In Georgia that will be particularly hard to prove, ironically, because of the voting machines being so terrible. I've been complaining about that for years. It will be ironic if Brian Kemp is now unable to prove a fairly large degree of fraud because of his own failure to upgrade to more secure machinery.
Another possibility that occurs to me: at least some of the swamp-creature Congressional Republican leadership is in on the scheme. They've agreed to let the Biden race be stolen in order to get rid of Trump, who is a problem for crony DC types of all parties. However, a condition is that the fraud can't be used to unseat any Republican Congressmen. Those races have to be run straight, or else they'll blow up the game.
The first possibility is one of a party engaged in fraud, in a hurry, while their party machinery buys them time with delays. The second possibility is of a self-appointed ruling class attempting to purge itself of an unwanted democratic element, and to reassert its control over the Federal government.
Are there non-fraud explanations that might be plausible? Lots of voters who know only about American politics that they hate Trump, so they showed up to vote in just one race on the ballot? But only in swing states? One possibility is that these numbers are wrong, and that we'll see in the final analysis that there wasn't such a discrepancy; but if that's true, then why didn't the Biden landslide also carry the Senate?