If you do a full text Solr search on api.drupal.org, you can filter by Project and by Core Compatibility but not by Branch.
It seems like filtering by Branch would be really useful. For instance, look at
https://api.drupal.org/search/site/%22will%20be%20removed%20in%22?f%5B0%...
there are a lot of duplicates in 8.0, 8.1, 8.2, etc.
I believe that the api_search sub-module supports a Branch facet -- it looks like our Solr implementation on api.drupal.org is simply not using it, or at least if it is, it's not being shown on the sidebar.
Closed: outdated
1.0
User interface
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
The new site is already live on Drupal 10.
We have search API and facets and we offer facets for core versions and other filters.
https://api.drupal.org/search/api?keys=test
Note that we also cleaned up a while ago branches per major, so we only have one.