So from shadowbaned user X perspective - everything looks normal. They can post, they can see own messages and they are "happy users".
From all the rest perspective - posts of user X aren't visible (they goes into "moderation" queue). So normal users don't see them. They can keep disusing and they are not aware that user X post anything.
From Admin / moderator perspective - Posts user X are visible like "Awaiting approval" with "Dismiss Flag" and they can be marked as "shadowban". Admin can still approve it if they are OK π
Clue is - as long as user X don't logout / login as different one - won't ba able to notice that his posts aren't visible to others. He / she will just think that everyone around just ignore his / her posts and "don't feeding" troll.