Adding specific metadata to the datagrid without configurations in Metadata-management or Mappings

It is currently only possible to add metadata-fields to the datagrid if they are part of the mapping- or metadata-management-configurations for a specific library. However, when migrating documents from an old DMS to the DMS Online, other valuable metadata-values might land in SharePoint that should be presented in the datagrid, while the metadata should not be part of the metadataform for document-upload (as a result of metadata-management configurations) or any field-mapping.

As such, it would be desirable to add specific metadata to the datagrid of specific libraries to present the migrated data that is available in SharePoint Online without having to use the metadata-management or the mappings for those libraries.