The overall brightness range for my 2020 Macbook Pro 16" was seemingly permanently lowered across the adjustable range after clicking the Display Brightness option below.
I now have to set the brightness slider to the maximum level for a sufficiently bright screen for daytime use (not on battery power). The overall adjustable range now lies much lower than before.
Neither the "Automatically adjust brightness" option in the Display preferences panel nor the "Slightly dim the display while on battery power" are able to reverse this, or even a restart.
Thanks for any insights.