>>495280124 ways
First is to just encounter one normally in the wild
Second is to go to an outbreak (Save at Jubilife, go to desired outbreak, catch/defeat all mons until shiny appears, if no shiny soft reset then repeat)
Third and fourth are just advanced forms of the second, outbreak chains and multiple outbreak chains
Here's a good vid to explain it all, this lucky got 2 shinies just doing the video:
https://www.youtube.com/watch?v=fxUqxIgiZew&t=678s 
