Elevation required for installation
When you install Vivaldi on a Windows PC it insists on requiring elevation. But your default installation is per user. As I run as a non-administrator I cannot install Vivaldi in my normal user profile without installing it for all users. The installer should only request administrator elevation if installing for all users. The Chrome browser does this nicely by falling back to per user if admin rights are not granted.
+1. This really is an issue.
Although there is a workaround - use 7zip to unpack the .exe install file and then unpack the vivaldi.7z file. You get the fully operational browser without any admin prompts.