The error/issue doesn’t seem to be related to the software part of discourse.
From my expirenece with SEO/Google search console, I can tell you that this is probably realted if you have redundant categories/tags.
For example may be you have categorey A, B:, and you have topics 1,2,3. Where topics 1,2 and 3 belongs to category A and B. This would lead to that category A page is identical to that of category B. Thus Google index would see redundant page.
What I said also can apply to tags, or any property that can lead to the creation of a page.
So of the top of my head I would say, ensure that you don’t have duplicate content by being catious with the usage of tags/categories.
A practical example from your site:
https://howtodiscuss.com/tag/queryhttps://howtodiscuss.com/tag/queryhttps://howtodiscuss.com/tag/querieshttps://howtodiscuss.com/tag/queries
Those two pages return identical content which is not so good for SEO and is related the issue raised above.
If you would want more in depth analysis of your site, or/and developing a functionality that can automicatlly mititgate that, I am happy to be counsltned. DM me or reach out at mailto:ghassan@zaat.dev.