I still don't understand this, sorry. Obviously you need to use a proper specification:
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Post, or
message, is a single piece of text
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Topic, or
thread, is a collection/list of related/grouped messages
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Forum is a collection/list of related/grouped topics
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Forums are your community, in whole.
So what should not appear and where? What kind of 'posts'?
If you talk about a single topic excluded from the Recent Discussions, it's not possible on the topic's level. Only a certain Forum could be excluded from the Recent list, you may take a look in
Manual how it's done. Probably, you could create a single Forum, where to collect all such "excluded" topics - that's the only way.