Copy and pasted from the documentation:
Read photo metadata using only ExifTool: To read photo metadata (including image thumbnails), the default is to use Exiv2, relying on ExifTool only when Exiv2 does not support the file format being read (e.g. Exiv2 cannot read CR3 files).
Regarding using a self-compiled version of exiv2, you need to ensure that gexiv2 is using your compiled version, not the system version. You need to figure out how to do that.