A great browser, but
really want to see it in the Extension Manager as to remove them manually is not a pleasure . sorry vivaldi://chrome/extensions
Anyway there's the item under the tools menu.
no. it is not there
What browser are you using?
It's there, just be sure to always have the latest snapshot installed
Extension manager can be called by Ctrl Shift E , too!
And with both menus Extension manager can be found under Tools -> Show Extensions
Install latest snapshot from https://vivaldi.net/en-US/