Manually saving metadata to files creates the entries indeed, be it in RGB files or in XMP sidecar files. The same thing works for DOP sidecars.
As pointed out many times already, I set DPL to NOT read/write/sync settings and metadata, which lets me control the interaction with Lightroom Classic, my “single point of definition” for metadata.
Manual control is somewhat annoying though: There are no keyboard shortcuts!
Moreover, it would be nice to have separate checkboxes for reading and writing metadata in DPL’s settings. Vote for the respective feature request I posted in 2022.