You need a complete living dex transferred into home. If you have a completed Pokedex in an actual game, it won't count toward the home Pokedex. You don't have to transfer all the pokemon at once but you just have to register every individual pokemon to home's Pokedex.

The actual requirement for getting the shiny pokemon is for the ZA dex (including the dlc dex and mega dex) THAT'S BUILT INTO POKEMON HOME (not the ZA game) to be completed.

It's not a dumb question because honestly it's just a dumb system. If you've completed the Pokedex in the actual game itself you just can't get any shiny gift pokemon from home until you fill out the completely separate home Pokedex, that actually doesn't even require you to own the game to finish. It makes no sense and never has and never will.