My friend and frequent co-author Bill Frey has crunched the county numbers and provides great descriptive data on where shifts toward Biden took place both overall by county type and within key states. There is much to be learned by looking at these data in terms of the diversity of areas that moved toward Biden, particularly in the Rustbelt. Urbanized cores of big metros and rural areas conspicuously did not join the party. (Note small metros are defined here as those outside of the top 100 in country.)
I particularly recommend tables A and B for scrutiny as they provide detailed demographic and margin shift data for the country, for key states and for counties with these states' large metros. Much to ponder here.