Shadow-banning individual posts ("Visible to self") is relatively unusual and acts as a demotivator to publish controversial content because such content doesn't drive engagement, as is actively demoting entire classes of content (like critical commentary on politics) from the start.
This approach seems to help ensure that there won't ever be a subculture on their platform that grows, becomes controversial and at some point considers it their right to use the platform for their controversial content, avoiding all the outrage that late introduction of moderation brings with it. (see Twitter)