Behavior of Photos in various scenarios

Import

On Catalina/10.15.7, importing a photo by dragging it into Photos will set Title, Description, and Keywords from XMP fields. Photos does not appear to read IPTC fields. These same fields are set when importing a photo via AppleScript.

XMP:Title --> Title
XMP:Description --> Description
XMP:Subject --> Keywords

Export

On Catalina/10.15.7, exporting a selected photo using the File > Export > Export 1 photo sets the following fields:

XMP:Description --> Description
XMP:Title --> Title
XMP:Subject --> Keywords
XMP:PersonInImage --> Person in image
IPTC:Keywords --> Keywords
IPTC:Object Name --> Title
IPTC:Caption-Abstract --> Description

When exporting with File > Export > Export Unmodified Original > Export IPTC as XMP, the following is exported. The XMP:Subject is set to the union of Keywords and Person In Image.

<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 5.4.0">
   <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
      <rdf:Description rdf:about=""
            xmlns:dc="http://purl.org/dc/elements/1.1/"
            xmlns:exif="http://ns.adobe.com/exif/1.0/"
            xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/">
         <dc:subject>
            <rdf:Seq>
               <rdf:li>Keyword1</rdf:li>
               <rdf:li>Keyword2</rdf:li>
               <rdf:li>PersonInImage1</rdf:li>
            </rdf:Seq>
         </dc:subject>
         <dc:description>Description</dc:description>
         <dc:title>Title</dc:title>
         <exif:GPSSpeedRef>K</exif:GPSSpeedRef>
         <exif:GPSSpeed>0.42</exif:GPSSpeed>
         <exif:GPSTimeStamp>2022-06-26T20:35:30Z</exif:GPSTimeStamp>
         <exif:GPSImgDirection>161.99160777000003</exif:GPSImgDirection>
         <exif:GPSLongitudeRef>W</exif:GPSLongitudeRef>
         <exif:GPSAltitudeRef>0</exif:GPSAltitudeRef>
         <exif:GPSLongitude>118.42</exif:GPSLongitude>
         <exif:GPSLatitude>33.42</exif:GPSLatitude>
         <exif:GPSLatitudeRef>N</exif:GPSLatitudeRef>
         <exif:GPSImgDirectionRef>T</exif:GPSImgDirectionRef>
         <exif:GPSAltitude>42.5</exif:GPSAltitude>
         <exif:GPSHPositioningError>12.42</exif:GPSHPositioningError>
         <photoshop:DateCreated>2022-06-26T13:35:30-07:00</photoshop:DateCreated>
      </rdf:Description>
   </rdf:RDF>
</x:xmpmeta>