On Macs Cmd+Tab cycles through Apps - there is one active window for a given app.
If an app has several windows (not tabs) it is standard to use Cmd+` to cycle through them.
This does not work in Vivaldi. Hence the request.
Without this it is very uncomfortable to have more than one window open in Vivaldi.
@Xijit Was this topic originally posted in the Webmail category?
Just upvote the existing feature request to support it. Duplicating feature requests makes extra work for the forum volunteers, and contravenes the instructions for creating new requests.
Help on Feature Requests