@swnt, Vivaldi is Chromium based (Blink). Never had any problems with Vivaldi in any page, but I know that some pages us the discriminating Browsersniffings, which should be illegal, but even with this I never had a problem, because Vivaldi appears by in their UA as Chrome, ever since Vivaldi removed their branding from the UA a few years ago because of these criminal practices of some pages.
Now in the Desktop browser you can even use BingChat, because Vivaldi automaticly switch its UA to EDGE