This script has been used to import over 50,000 Google+ posts
and over 300,000 comments from 29 communities into a single
Discourse instance, as well as for at least three other
imports.  Google+ has closed for the public, but it is still
available at this time for GSuite customers. If GSuite customers
decide to migrate from Google+ to Discourse, or if Google
"sunsets" Google+ for GSuite customers, this importer may be
useful.
https://www.reddit.com/r/FMGE_Support/comments/b8sa5h/fmge_for_gsuite/

Development and use of this script has been discussed in detail:
https://meta.discourse.org/t/bounty-google-private-communities-export-screenscraper-importer/108029