Vivaldi claims to be a privacy browser, but it pushes ads to the users whenever possible. For example, the start page tab is filled with pages that have their affiliate links, without asking for the user’s consent. Vivaldi’s ad blocker also whitelists ads that generate revenue for Vivaldi, again without the user’s consent. Moreover, Vivaldi does not have a setting to disable JavaScript; users would have to access the default Chrome settings to do that.( also they keep saying that they don't want to opensource their browser because then they would fail, while this is very wrong as proven by other opensource browsers)
Overall, I think they are very scummy when it comes to privacy and ethics of consent of ads/affiliation.
Their ads are still far less invasive than Edge or Firefox (and especially the latter). As far as I know the default links are all just typical paid defaults. And yeah, it's irritating that the ad blocker has those defaults and that they won't open source more of their stuff. But I still think it's far better than what other browsers have going currently
Almost all of those are developed part time as hobby or side projects. They aren't built on the same scale as other commercial browsers, and a few of them aren't even trying to.
Also, these are all browsers that are deliberately privacy focused, and are made towards a different audience than Vivaldi. Not to mention that advertising isn't always inherently privacy invasive. It's just intrusive.