Since all of your voltages tests appear to be normal, and the tests by the shops have show that everything is working correctly, it is understandable that you are perplexed. I would be too..
Perhaps your best approach would be to get a good understanding of the charging circuitry in the 4Runner. The "battery" light in cars is really turned on by the voltage regulator circuitry and has nothing to do with the battery it's self. Perhaps looking trough the diagnostic steps in the 4Runner repair manual would help:
TOYOTA 2016-2019 4Runner Repair Manual RM27F0U