@LonM I"m not aware you can sync with IOS or android fully so that the main OS apps are no longer needed. I tried syncing on windows and a Mac and gave up in frustration. It would be that Vivialdi sync automatically (or after answering a few questions)
the GOAL would be... when Vivaldi could sync data seamlessly across all platforms with the core communication apps (mail, contacts, calendar,and the host use functionality os no longer required.
usability is the key. it make syncing and app use easier in single cross platform app. there is also a host a integration needs such as phone dealing from contacts that would be needed.
I don't think Vivaldi provides that seamless data integration at present. mobile and desktop needs differ greatly.