I'm not sure exactly what you mean by "these services/libraries", but yes, in Solid, apps need to be explicitly built to support Solid, and data can only be sto

I'm not sure exactly what you mean by "these services/libraries", but yes, in Solid, apps need to be explicitly built to support Solid, and data can only be stored in Solid Pods. Although it's not Solid, an older project is https://remotestorage.io https://remotestorage.io, which is a library that needs to be explicitly used by apps supporting RemoteStorage, but does allow users to store the data on Google Drive or Dropbox too, IIRC.