Use at your own risk.
Chunk banning is making a chunk or area have too much data for servers to send to the client, so it is forced to kick you off the server if you are near enough to the chunk ban. There are two methods of chunk banning; the first is the method of building high NBT structures, although this does not work in recent versions. The second (and more reliable) chunk banning method, now known as area banning, is to fill a shulker box with high NBT books and drop it as an item entity. Unlike chunk banning, this will kick you from the game if you are within 75 blocks of the dropped item on a Vanilla server, or 32 blocks on a server with Spigot/PaperMC server software.
Chunk bans are mainly used in anarchy servers, prisons and safe houses to keep people out of certain places. The first reference of a chunk ban was the furnace chunk ban in 2b2t, and the first non-anarchy reference was in a prison called The Obelisk by Miningblob. Ever since then several prisons and safe houses have been made with dropped shulker box area bans, most notably Gaia's Vault by SeenSven+TheDeafCreeper and Wifies' safe house.
There is a lot of misinformation about the difference between Chunk bans and Area bans; so watch this informative video by Jerrylum to fully understand Area Banning.
DO NOT hold it in your inventory if playing on 1.18.1 or higher. it will PERMANENTLY ban you. The solutions are either to change the nbt data in the server/world file to remove the shulker box or to have a friend place a repeating command block with "/clear @p shulker_box" near you and then try to join.