They only give you 1 shot to throw a ball or the Pokemon disappears. Does Sw/Sh follow Pokemon Go's example and make them a 100% guaranteed catch?
It is not a guaranteed catch, but it is guaranteed to always be shiny (when it comes out as shiny). I just had 3 attempts at a shiny Gigantamax Butterfree, and it was shiny every time even though I didn't catch it the first two times