Alright, so this is Biden's dream scenario, and there is a good chance it'll play out, but there are several *s.
Trump's hopes boil down to PA and FL. Biden holds a good led in PA, but FL is narrower.
Trump is solidly down in AZ and NC, which weakens his position a lot.

Here is another map in which Trump wins AZ and the south save VA which is nearly impossible for him to win. Trump still is defeated but it's tightened. It should be obvious what needs to cave for a Trump victory: PA

If Trump takes PA, where he's currently down by almost 5 points, it becomes a very very tight race.
Now we'll briefly get into the extremities that could happen.

While Biden is up in several states, it's possible it could take weeks for mail in votes to be counted, which means on Nov 3rd, it could look like Trump is winning.
This is where concerns over accusations of voter fraud arise, especially if Trump feels its his path to victory.