TL;DR: 3,332 posts from multiple communities have links to productforums.google.com. Source. Apparently all these links are "broken" (they are redirected to the homepage of a community hosted in support.google.com). Suggestions?
Google has a lot of products. Over the time they have restructured the product group organization and how they support them. Some products have used Google Groups from a long time others used Google Groups then changed to Google Groups for Business with a custom domain, productforums.google.com and nowadays host their currently called communities in support.google.com.
Some posts have quotes / summaries, they might OK be regarding the self contained rule but there are many than not.
I have already tried the Wayback Machine (archive.org) for posts from Web Applications that were bumped or bring someway to mod attention (flag, review queue, etc.) but didn't find any.
Questions having a link to productforums.google.com that have not being update on any of it's answers since 2016 (?) it's very likely to be obsolete. Depending on the community, probably in Web Applications, Android Enthusiasts, Ask Different, the posts might not be helpful for anyone anymore.
These "broken" links are not found by using http errors as is done in Characterizing broken external links on Stack Overflow. Instead use a search with