I noticed that the datetimes exifr provides are offset by some number of hours from the correct time. The times provided by exifr are two hours before the local time where the photos were taken. Perhaps this is related to the fact that the time zone of the system I'm using to read the data is currently two hours ahead of GMT.

Here is the relevant data from a photo read by exifr:

ModifyDate: 2021-08-28T07:02:40.000Z
DateTimeOriginal: 2021-08-28T07:02:40.000Z
CreateDate: 2021-08-28T07:02:40.000Z

And with exif-reader (these are the correct local times):

ModifyDate: 2021-08-28T09:02:40.000Z
DateTimeOriginal: 2021-08-28T09:02:40.000Z
DateTimeDigitized: 2021-08-28T09:02:40.000Z