All the postal votes that came in over the weeks before election day were all held.
They are a laborious process to process, but it's done and properly. Many states are not legally able to start the processing until election day.
They were counted AFTER the election day ballots.
There are observers at all times.
Results are often published in large amounts together. This is the US, there is a LOT of population in some places.
Funnily enough, this is the almost identical system we use in Australia.
Biden didn't "magically" pick up 700k votes to fulfill your conspiracy theories. Biden got 700k votes from the postal votes that were sitting in the election commissioners storage space that could not be counted until the last few days.
Suggestions of badness otherwise, without evidence remain baseless. That's why all the legal cases have been laughed out of court so far. The sole win, was for observers to stand a bit closer - in no way a reputidation of the election system.
