Multiboxing is not against the ToS. But keycloning should be.
And before any of you make the argument ‘whelp guess we gotta ban addons if you want that’, I dont seem to recall any addons that specifically allow you emulating another person entirely. And if an ingame addon like that did exist they would likely break the coding for it like they did with shard hopping the way it worked back in Legion
And before you say something stupid about me being another character from the same person, how about you check my achievement count and compare it to the OP? Did I cover all my bases?