I tried opera a while back, and while it's fast and looks good, it has a new tab page with "recommended" sites that you can't turn off - I tried, but it's protected by DRM (opera will refuse to start if the file doesn't have a valid digital signature).
So if I'm going to switch browsers because of privacy/advertising concerns, it's not going to be Opera.
I mean... at least it has mouse gestures. Hard to knock it for being not feature-rich enough when it has a feature no other browser has by default (except Vivaldi, which has Opera lineage).
a) This built-in feature is way below the standards trivially achievable via extensions in Firefox, Chrome etc.
b) It's a downgrade in relation to what Opera itself used to offer in the past (and then, if I recall, got so stripped of functionalities it didn't even support bookmarks at some point).
The new tab page has a list of bookmarks you can customize. It starts off with some "recommeded" sites in there, but you can just remove them once and they never come back. The only thing you can't remove from the new tab page is the Google search bar, which never really bothered me. Either way, it seems like you're implying that Opera will populate the new tab page with sites it chooses, but that's just not the case.
It is described under the "new tab page" section. I can't really comment on the privacy/advertising concerns but I do know that Opera providers a VPN for you (who know what they are doing behind the scenes) and have their own adblocker built in.
I don't see anything like that in new tab page. I have only searchbar and thumbnails for pages I like to visit. I'm on Mac, do they have different versions of new tab page for other systems?
So if I'm going to switch browsers because of privacy/advertising concerns, it's not going to be Opera.