Rather than speculate, look at the polls from Real Clear Politics vs. the actual vote counts.
Final RCP Average in PA: Biden +1.2. Actual election result: Biden +1.2.
MI: Polls Biden +4.2 Actual Biden +2.8.
GA: Polls Trump +1.0 Actual Biden +0.3.
NC: Polls Trump +0.2 Actual Trump +1.3.
AZ: Polls Biden +0.9 Actual Biden +0.3.
WI: Polls Biden +6.7 Actual Biden +0.7.
NV: Polls Biden +2.3 Actual Biden +2.7.
So the only state among the close ones that was really off was Wisconsin. Which had a similar discrepancy four years ago.