Removing google accounts
Probably obvious, but can't find an answer: Under Chrome I can go to chrome://settings/ and then choose which accounts I can register to automatically sign in when accessing google apps like gmail. I can't find the same "sign in" option to manage my accounts in Vivaldi, although the accounts are indeed there: I can see them when, for example, I click on my avatar in gmail.
Any thoughts on how these accounts can be removed in Vivaldi?
Of course the accounts are "there". You made them at some point and they are accessible on the internet. You can access them with any browser. The only thing you can do with Vivaldi is save passwords for them. You can review/delete those in vivaldi://settings/privacy/. But check chrome://settings in Vivaldi yourself, the site exists.
Vivaldi doesn't connect to Google Chrome Sign In (yet).
No extensions or apps that need Google Chrome Sign In will work in Vivaldi.
However, the button you're talking about is in
chrome://settings(as mentioned by @luetage).
It's named "Sign in to Vivaldi".
That won't work as you expected like in Google Chrome.
Remember, Google Chrome Sign In & Google on the Web Sign In are different.
Based on above, are you sure that last Gmail your talked about is Gmail in app?
Sorry, the fact of Google Chrome Sign In & Google Web Sign In always confusing. This brought...
About removing Google Accounts, do you mean "really" remove it or actually to Log Out?
Really remove it is in your Google Account on the web settings. You'll lost your Google Account this way.
Log Out, it's in your Google Avatar. Or, just clear your Google Cookies.