luceos Mass Actions is currently only for the discussion list, but the idea was definitely to add it to the discussion post stream, profile post stream, user directory and admin user list as well. I have not had time to work on that yet. If someone wants to sponsor the feature, feel free to reach out.
Depending what posts you're trying to delete, Mass Actions might not help. Are all the posts in the same discussion? By the same user? Or just some common keywords or timeframe? Maybe a better UI would be one where you manually type filters and it selects the discussion to modify.
If we had post search rather than discussion search in Flarum, then Mass Actions could simply be added there as well to benefit from extension-provided filters or simple keyword search.
