That's my gut feeling.
I don't think it's at all impossible for Biden to win, but that's my gut feeling.
To be more specific: I think the "Red Mirage" scenario will happen. Trump will have a lead on election night and he and the Republicans will pull some fuckery to stop mail-ins from being counted in the right places.
If it gets to the Supreme Court, either Biden and the Dems will pull a Gore and surrender the election without a fight, or the Court will rule in his favor and hand him victory.
History will repeat itself.
What they fucked with was the USPS, not the way mail-in votes are counted (generally, they did get a few court cases here and there to limit mail-in counting). And I don't have numbers for this, but I'm pretty confident most of those mail-in votes have already arrived, and there are way more in-person early votes than mail-in.