BTW - I would be surprised if Capture One could modify IPTC etc metadata for an HEIC without doing this in a sidecar file. I think C1 will leave the file unmodified.
What happens in this case: 1) edit metadata in PM; then 2) edit photo in Capture One, there will be an XMP sidecar.
When PM finds an XMP sidecar paired with an HEIC, PM will compare the modification times of the HEIC and the XMP sidecar. If the sidecar has a more recent modification date, the assumption is that this has all the updated XMP, and that will be loaded instead of from the XMP embedded in the XMP.
HOWEVER, when PM then saves out new modified metadata (e.g. just changing rating), PM should delete the XMP sidecar file because it isn't necessary.
--dennis