Feature Requaest: 3rd Party Cookie Exceptions
While the option to turn off third party cookies is grand and lovely, some websites demand them - Ubisoft won't let you log in without a 3rd party cookie. Adobe needs one to handle logins and authentication. BBC iPlayer can't save your favourites without it.
Chrome gets around this by having a whitelist for domains,
Could Vivaldi get that feature?
You can add exceptions on chrome://settings/content, though I haven't tried it yet. Can you try this and let us know if it worked for you?