投稿コンテンツの一部を「ログインして表示」または「返信して表示」機能で非表示にする

[Jagster (Jakke Lehtonen)]

You can show name of a topic and hide topic itself showing request to login, but I don’t know any ready-to-use solutions hide only partially.

This is doing almost wanted, but then all categories should be with limited access. But that you are looking for.

Advertise activity in a private category (discourse-category-lockdown)

This plugin allows you to restrict access to topic pages in a category. Topic titles will still show up in topic lists, search, user activity & digest emails. This is a great way to advertise the activity in a “members-only” category, which may charge for access. It IS NOT designed to keep the contents of the category 100% private - if someone is determined enough they will be able to piece together the content from search results. Each category has a couple of new settings in the Security tab…

@Dennis_P_Z

or to users who have not replied?

If so how could anyone reply ever then? It would hide that topic then for everyone but OP.