Related to my previous comment.
I finally managed to connect Opera on iPhone and linux PC.
How to:
- Remove Opera on iPhone
- Install Opera on iPhone again
- Delete My Flow on PC - that harder delete - reset
- Run Opera on iPhone and go to connect PC - follow the steps as described.
As I was desperate I even did the emergency reset of My Flow on the PC.
But I think, the reset on PC is necessary and after the unsuccessful connection the Opera must be reinstalled on iPhone.