The implementation of these interfaces for Windows PDBs is provided by Microsoft.DiaSymReader.Native package. The implementation for Portable PDBs is provided by Microsoft.DiaSymReader.PortablePdb package.
It is recommended that new applications and libraries read Portable PDBs directly using APIs provided by System.Reflection.Metadata package. These APIs are much more efficient than DiaSymReader APIs. Microsoft.DiaSymReader.PortablePdb bridge is recommended for existings apps that already use DiaSymReader APIs and need to be able to read Portable PDBs without significant changes to their source.
Pre-release builds are available from Azure DevOps public feed: