I think if Biden rallies his base, but remains unpopular, he gets 48% of the vote. That's generally where weak D's have ended up at, right? I don't think Trump gets 10%, but he might get 6% and a Libertarian might get 1%. That would leave DeSantis with 45%. It would basically be 2016, but with a spoiler exclusively on the Right.
It would still be close. My guess? DeSantis wins Pennsylvania, Nevada, and Wisconsin, but still loses Georgia and Arizona. I think Biden wins by winning North Carolina because I don't think DeSantis will do particularly well with black voters though he probably maintains Trump's coalition in other areas.
Zero chance of this happening even if Trump wins only 6%.
And I actually think Trump would get a lot more than 6%. It might be more like 1912 - Trump probably won't do as well as Roosevelt did, but he'd be a Republican ex-president who got jilted for the nomination, and thus ran as a third-party/independent spoiler candidate who cost his party the race big time by performig well. In terms of exact percentage Trump would win 12% of the vote, at least (I think 20% is pretty possible).