Remote attribute in mymodule.libraries.yml
According to the code/comments in LibraryDiscoveryParser::buildByExtension, it's to help ensure licensing info is included for 3rd party libraries:

// If this is a 3rd party library, the license info is required.
if (isset($library['remote']) &amp;&amp; !isset($library['license'])) {
  throw new LibraryDefinitionMissingLicenseException(sprintf("Missing license information in library definition for definition '%s' extension '%s': it has a remote, but no license.", $id, $extension));
}


It's also mentioned in the library docs, but it just says that it's a good idea to include the remote info, not why. It doesn't appear to be used in the code other than the licensing, so I think it's safe to assume it's a reference/info value for now. There is no incorrect value to-to-speak, but it would make sense to set it to the URL of the project you're referencing.