I have most of the Pokémon in the Scarlet/Violet Pokédex, but do I have to catch 'em all, or can I just see them?
A "complete" Pokedex is one that has captured every Pokemon, excluding mythicals. This is how the player obtains reward items like the completion diploma and the Shiny Charm. There are two notable exceptions:
To the best of my knowledge, every Pokedex reward in Scarlet and Violet comes from capturing Pokemon.