I installed the latest version of the Vivaldi browser on macOS and after a reboot I found this on my dock:
Normal? No, I did not put it as default browser, I did not stick it in the dock and especially I did not leave it open (the white dot indicates that it is running)
So, somewhere, there’s some setting that launches it automatically every time you start the computer.
But my main browser is Firefox, I use Vivaldi only in limited cases, where the site works well only with Chrome. (I try to use Google products as little as possible, Vivaldi is like Chrome but without Google user tracking).
I’m looking everywhere for this setting, but I can’t find it.
Finally, I found it in “System Preferences” -> “Users & Groups” -> “Login Elements”.
You must press the “-” button to remove it from automatic start. Not on “hide”.