I saw this tip online about getting the ‘rare’ mystery islands, I’ve tried it 3 times and it worked 2 out of 3 so could just be coincidence!
(Rare includes any that aren’t a just basic islands including bamboo island, money rock island, second fruit island, tarantula island etc)
Approach Orville but end the conversation
Then use the joy reaction until he does it back to you
Then cross your fingers as you travel using a NMT :) hope this helps!