Upleveling David's comments to mark as official answer.
The following behavior described as a bug, is actually as designed:
"...do nothing and hit 'Done', then an XMP sidecar file is written to disk. But if I open that sidecar in a text editor and check what's in it, then the preset settings aren't written in there."
Camera Raw does not add settings to a photo until you actually make an adjustment. This is as designed.
I understand there are manual steps required to commit the
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