Some caution on that poll is that it doesn't properly weigh for education, so could be skewing Biden's way by over-counting college grads.
But this is very notable, too and the opposite trend compared to 2016, just much more pronounced.
Polling is again pretty much meaningless, because their methodology is wrong as you correctly point out.
Enthusiasm amongst Republicans and Trump supporters is at a all time hi. Trump can have a rally at any stadium tomorrow and it will be full.
Biden on the other hand will struggle to fill a town hall if his Democrat handlers trust him enough to read a speech, which is unlikely.
The strategy now is to keep Bidden hidden because every time he goes out in public he'll make some "gaff" that will just make him look more like an unelectable old man with dementia.
Young people won't vote they don't care now that their candidates are out, they didn't even vote when their candidates had a chance.
The only people still voting are the lifelong Democrats that will always vote no matter who is the candidate and never Trumpers.