Cathas9lives how familiar are you with Flarum extension API ? Have you already made any frontend or backend extension ?
You could preload the discussions by adding a new relationship to the Tags serializer, then read that data from the frontend via a relationship, or do an API request when necessary to fetch the discussions, by hitting the same endpoint Flarum uses for the discussion list, with the tag:
gambit to filter which tag to show. Either way you'll require at least extending one javascript component of Flarum.