I cannot access the internet via Vivaldi but can with Firefox and IE. Error messags are e.g.: This site can’t be reached The webpage at http://www.aol.co.uk/ might be temporarily down or it may have moved permanently to a new web address. ERR_INVALID_ARGUMENT. Any ideas why Vivaldi is discriminated against? Usimg Panda for security.
The last four words of your comment may be the answer.
As Vivaldi is new, a large portion of the 3rd party "security" software community cannot be bothered to inform themselves and their software that it is a legitimate app, allowed to access the internet and to write to files on the computer. They target it as malware and block various of its functions including, at times, the mere action of starting up.
Rarely, Windows firewall or Windows Defender have even blocked it.
Usually, both Windows and 3P "security" software will allow you to whitelist the .exe.
False positives can be reported to software vendors.
On the other hand, if you use any sort of proxy which is not set as the system default, Vivaldi might not be able to access the internet because it can, for now, only use the system default proxy protocol.