One of the answers to this question (Google Earth Engine - Get Image with highest max Scene NDVI from a time period) provides code which gives a Sentinel image/date with the highest NDVI for each region (https://code.earthengine.google.com/5165eca22f5dbfc8e114919d9315ab73).
This is half of what I want, but I also want the Sentinel image/date of the lowest NDVI for a region, but am not sure how. I have tried changing
return ee.Feature(meanFeatureCollection.sort('mean').first()
to descending order, but it didn't change the console output.
EDIT: I double checked and the link code doesn't actually do as described, it only prints the NDVI and ID of first Sentinel image in the collection. So I also need the correct script to identify highest AND lowest NDVI images.