Where has "com.adobe.folder" gone?

"com.adobe.folder" still works. You can see all the metadata-field tokens by going to the Metadata panel, selecting the Default tagset, and clicking the Customize button at the bottom. Select the fields you're interested in.  Your selected fields will be saved in this file (or its analagous path on Windows):

/Users/john/Library/Application Support/Adobe/Lightroom/Metadata/DefaultPanel.lua

For example, here are my current settings, including "com.adobe.folder":

list = {
"com.adobe.filename",
"com.adobe.copyname",
"com.adobe.fileFormat",
"com.adobe.folder",
"com.adobe.filesize",
"com.adobe.sidecars",
"com.adobe.audioAnnotation",
"com.adobe.caption",
"com.adobe.userComment",
"com.adobe.captureDateTime",
"com.adobe.metadataDate",
"com.adobe.imageFileDimensions",
"com.adobe.imageCroppedDimensions",
"com.adobe.make",
"com.adobe.model",
"com.adobe.software",
"com.adobe.lens",
"com.adobe.focalLength",
"com.adobe.focalLength35mm",
"com.adobe.exposureProgram",
"com.adobe.exposureAndISO",
"com.adobe.exposureBiasValue",
"com.adobe.flash",
"com.adobe.GPS",
"com.adobe.GPSAltitude",
"com.adobe.ratingAndLabel",
"com.adobe.metadataStatus",
"com.adobe.preservedFilename",
"com.adobe.originalFilename",
"com.adobe.subjectDistance",
"com.adobe.title",
"com.adobe.FNumber",
"com.adobe.apertureValue",
"com.adobe.altTextAccessibility",
"com.adobe.extDescrAccessibility",
"com.adobe.dng.bitsPerSample",
"com.adobe.dng.floatingPointType",
"com.adobe.exposure",
"com.adobe.lastExportTimestamp",
"com.adobe.combinedCameraName",
"com.adobe.absoluteFilepath",
"com.adobe.filenameExtension",
}