Ultra Sun, easily. I can’t remember exactly how many, but I got
multiple from the Ultra Wormhole, including Abomasnow, Altaria, and
Crustle, and also caught a Bewear and hatched a Cubone.
I never found any shinies in any other game, except for Y, because
I did run into a shiny Druddigon there, but I accidentally knocked
it out, because the camera didn’t show it to me when I was
selecting my attack so I didn’t have the chance to see that it was
shiny until I’d already selected a move that would KO it in one
hit.
i have 542 shinies in pokemon go, but i don't count that
i think either ultra moon or let's go eevee has the most shinies, i
can't remember
"The phrase “it’s just a
game” is such a weak mindset. You are ok with what
happened, losing, imperfection of a craft. When you
stop getting angry after losing, you’ve lost twice.
There’s always something to learn, and always room
for improvement, never settle."
-Sun Tsu, The Art of Gaming
Definitely Shield. I have five boxes of shinies, some of which were
from other games but the rest was just straight up raids. It's
weirdly addictive. Usually Shield hosts my "passive" hunts while
I'm full odds hunting.
Still haven't gotten a shiny from Dynamax Adventures though!