No such thing. That suggests there is a centralized authority making that decision. It’s possibly that certain relays filter you out however or that clients are locally muting you for their users.
Discussion
How is the group of people making these decisions less centralized than the group of people making decisions for Facebook and reddit?
Because the Nostr protocol is decentralized. Everyone owns their own data and can move or access it from many places.
If you don't like a Relay you can move to many others.
If you don't like a client you can move to many others.
If you don't like Reddit or Facebook, you're out of luck, thats the only place you can access that data, and its not yours, its theirs.
I don't see how any of that conflicts with the definition of shadowban
And how is the level of centralization of the people making the decisions relevant to the definition of shadowban?