Since 1.25.0 (Release v1.25.0 · icloud-photos-downloader/icloud_photos_downloader · GitHub), icloudpd can retrieve icloud photos metadata as xmp-sidecar.
On Digikam 8.5.0, none of this data is retrieved and added to image information (Metadata > sidecars: read from sidecar is enabled)
Example data
$ xmllint --format IMG_0176.JPG.xmp
<?xml version="1.0" encoding="utf-8"?>
<x:xml_doc xmlns:x="adobe:ns:meta/" x:xmptk="icloudpd 0.0.1+abcdefgh">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description xmlns:dc="http://purl.org/dc/elements/1.1/" rdf:about="">
<dc:description>Icloud description/title</dc:description>
</rdf:Description>
<rdf:Description xmlns:exif="http://ns.adobe.com/exif/1.0/" rdf:about="">
<exif:GPSAltitude>123.472306143001</exif:GPSAltitude>
<exif:GPSLatitude>456.86674166666667</exif:GPSLatitude>
<exif:GPSLongitude>-123.37184166666665</exif:GPSLongitude>
<exif:GPSTimeStamp>2024-12-12T01:23:51</exif:GPSTimeStamp>
</rdf:Description>
<rdf:Description xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/" rdf:about="">
<photoshop:DateCreated>2024-12-12T01:12:51-0700</photoshop:DateCreated>
</rdf:Description>
<rdf:Description xmlns:xmp="http://ns.adobe.com/xap/1.0/" rdf:about="">
<xmp:CreateDate>2024-12-12T01:12:51-0700</xmp:CreateDate>
<xmp:Rating>5</xmp:Rating>
</rdf:Description>
</rdf:RDF>
</x:xml_doc>
Tried to do some conversion with exiftool but unclear which fields would allow an easier import.
Only dc:description and description:rating are non-existent in default icloud image export. Manual icloud export allows optionally to keep title/legend and location/gps.