In all generations since Shiny Pokémon debuted, there are a few species that cannot be legitimately obtained as Shiny. These Pokémon are commonly referred to as Shiny-locked. This can happen if the Pokémon is coded not to appear as Shiny in the wild, or via in-game gifts, in-game trades, breeding, or has never been distributed as Shiny via events.
In Pokemon Home you can deposit all 896 or so Pokemon for later use. Pokemon Sword and Sheild, Lets Go and Pokemon Go have different requirements for what they need.