Hi for all of you suffering from logging in for flow.
I had the same issue to re-log in to my account and Opera app does not either recognise my password or scan code.
I tried everything but rarely worked sometimes or never.
Go to "Opera.com/connect" then scan QR code from there.
If you scan the code from the flow on your desktop it would never work. Don't bother even reset synchronisation, you would only lose your data saved up on your Flow.
I heard that Opera belongs to a Chinese company now and it seems that there are not many developers working so no-one from the team is willing to tackle this simple issue even it has been a problem for at least 2 years.
I love Opera which is much simpler than Vivaldi or more features than Firefox but Opera could lose its users if they could not solve such simple issues.