Yeah, Biden won after the DNC rigged the election in favor of their candidates. Prior to that, Sanders was doing pretty good. Polling also had Sanders doing pretty good in red states.
Yes, the south is super racist, I know first hand. And I agree that the south would have been an uphill battle for Bernie, but I think he could have won despite having the south against him. Now it's too late, and it's just speculation.
But none of that takes away from the fact that the Democrats keep putting up terrible candidates that nobody wants. Look at the polling and votes for Harris, Biden, and Hillary. They did terrible, and it wasn't a surprise to anyone. The Dems need to pick better, or they are gonna keep losing.