@ynooue Hey, I ran into the same thing when I switched to iPhone recently.
What sort of worked for me was:
1. Logged into my Opera account on both devices at the same time (old Android and new iPhone)
2. turned on Sync under Settings > Sync and backup, the part with Flow and Bookmarks
3. wait…. I think I had to send something new in Flow to get it to kick in.
Not 100% sure if everything came over perfectly, but at least my recent stuff showed up…