Are member threads or comments indexed by Google?

Please check google search - use site: operator - example:

site:community.wpmanageninja.com/portal/

For Public Community and Spaces you have your sitemap.xml files generated so you can submit them to GSC:

https://community.wpmanageninja.com/portal/site-maps/index.xml

Read this thread:

https://community.wpmanageninja.com/portal/post/indexation?comment_id=26306

Check docs:

https://fluentcommunity.co/docs/create-an-xml-sitemap-in-fluentcommunity/

https://fluentcommunity.co/docs/generating-a-sitemap/

You can try to use search icon (top menu) and look for a SEO related previous discussions in case you are interested in finding some user challanges:

https://community.wpmanageninja.com/portal/space/community-meta/post/help-with-community-indexing