So finally after more years than I can remember goodbye to Opera as my primary browser. This issue on 2 websites and the fact that the browswer hangs requiring Opera to ended with task manager every few days with no fix in site helped me make my decision.
@cafeochomx
My about 40 tabs consume 800MB either. Is that actually a problem? I've got some gigabytes free, Opera could consume up to 6GB or so, I would not notice.
But as this 800 MB is for single tab and seems a bit too much, press Shift+Esc and note down, which Opera sub-processe consumes most memory. It is likely some extension, be it Opera internal or some external one.
@leocg I went into the install ("C:\Users\AppData\Roaming\Opera Software\Default...") directory and copied all the personal files. Then I erased the entire folder and everything in my system that was related to Opera, hoping a complete fresh install would solve the problem and give me an Opera that can use the personal files from before. I was able to restore all bookmarks and history installing GX, but the passwords did not reappear. Regular Opera still has the same problem of just not wanting to be.
I struggled with the same behaviour. You have to go to advanced settings. Switch of payment methods in autofill. In my setup its called "Zahlungsmethoden" and I simply translated, so real name of option may vary.
This is an old question, but the only answer I found by searching for "Opera + IBAN". If anyone will ever try this way again, the answer won't be "no way", while there is.