Okay, so from what I know the repeat ball works based on the fact that a Pokemon is registered as having been owned in your pokedex. With that being said, there are a decent amount of Pokemon in sword and shield not listed in the pokedex itself, so would a repeat ball still work? Thanks in advance!
Alright, I did a bit of research and made this topic on GameFAQs.
The responses I got basically said that if you somehow manage to get something like Necrozma in the wild, the Repeat Ball will not give you the multiplier. Anything in the standard Galar or Isle of Armor Dexes can receive the multiplier, however.
Hope I helped!