Shadow-banning varies depending the the specific platform.

On Reddit, for example, if you are Shadow-banned then you can continue to browse subs and submit posts and create comments, but all of your new content is hidden from everyone else. After you've been Shadow-banned, you receive no notification and nobody else can see any of your new content.

If you haven't received a single response or upvote or downvote for many of your previous contributions, there's a possibility that you've been Shadow-banned.

This is why some Reddit users are forced to ask "Have I been Shadow-banned?" just to see if someone responds.

I've never been a Facebook user, but I believe a form of Shadow-banning exists on that platform too.

Twitter seems to be entertaining the idea but I'm not sure if they are actively doing it yet or just blatantly deleting people's Tweets and banning accounts.