The Senate currently stands at 53R / 47D, so even if Biden wins the D's need a net +3 to flip control, with Harris as the tiebreaker. As of now, they flipped CO and AZ but R's flipped AL, so D's are currently +1 assuming they hold a very tight race in MI, and also assuming R's hang onto NC where they're more comfortably ahead.
Thus D's would need both GA seats to move to +3, which is quite unlikely, but would make for some crazy expensive campaigns, and would make me glad I don't live in Atlanta.