Or as I'd like to call it: THICC effect clouds can be used to soft-lock clients and/or permanently destroy your server's world! (if you don't know how to fix it)

Here is how it works:
1. Create a new world with commands enabled
2. Type the command:

/summon minecraft:area_effect_cloud ~ ~ ~ {Radius: 2.14748365e9}

3. ???
4. Minecraft client freezes, and only be fixed by a force stop with task manager

In singleplayer the effect cloud is deleted when restarting, as there is no way to save changes to the world (though if you did, that world would become unusable).

Servers do not crash, so using the above command will effectively render the immediate chunks on the server unusable until the effect entity can be removed via commands. And clients who come within render distance of the entity will freeze and crash.