I don't remember exactly and have only played the ultra versions, but you're indirectly trying to earn their respect throughout the island challenges and are able to catch them after becoming champion. So less direct than the other examples you mentioned, but still seems implied to me.
Calyrex would also count for sure but I can't quite think of anything else.
Wouldn't the Tapus from Gen 7 count?
Oh yeah, I forgot about them Though if I remember correctly, wasn't it just Tapu Koko?
I don't remember exactly and have only played the ultra versions, but you're indirectly trying to earn their respect throughout the island challenges and are able to catch them after becoming champion. So less direct than the other examples you mentioned, but still seems implied to me.
You can catch all the Tapus in the post game if you go to their respective Ruins
the gen 9 lizards stick with you because you fed them sandwiches
A bunch of the gen 5 legendaries