The following commands will produce a small application that allows you to run Vivaldi—or any other Chromium-based browser—in Standalone mode on a Mac. This could be used for testing a specific setup or version, without touching the system wide settings (profile). It can also be used to create a portable (USB install) of Vivaldi that you could store on an external disk, for sharing between computers.
Start Terminal and issue the following:
mkdir -p Standalone\ Mode.app/Contents/MacOS