It is clear that in 2016 Republican and Democrat absentee ballot behavior was identical, or nearly so across all precincts. That is, it varied by precinct, but within precincts it was much the same or either party. The percent plots was almost the same for any precinct in 2016, and it rose for both parties in 2020; however, it jumped much higher, and at a consistent rate in 2020, only for Democrats.
This is proved in the ratio plot. The D to R absentee rate across precincts averaged about 1 in 2016. Behavior in precincts differed, just as you’d expect, but overall there was no consistent difference.
In 2020, however, there is a marked and consistent difference, with Democrat ballots being marked as absentee at rates about 50% higher than Republicans. This is very strange, and most unexpected and not explained readily by simple changes in voting behavior.
Yes, both Democrats and Republicans were likely panicked and afraid of the coronadooom, and so more voted absentee. But were Democrats exactly 1.5 times as panicked and afraid everywhere? It beggars imagination.