I would like to see a link to Mail in the menu bar to forward current URL
Please make a feature request.
How to make a feature request for Vivaldi
If you think your problem can be solved by a missing feature, please add a request at https://forum.vivaldi.net/category/48/features-requests in the corresponding thread for your browser version.
And a link to do the same in Messages and FB Messenger. I often like to forward the URL that way!