Vivaldi forgets (preferences) zoom of websites, e.g. 125%, when opening Link in a new tab (100%)
zoom of websites often must adjusted to 125%, adjusted value in preferences is ignored, when link is opened in a new tab
Try changing the setting for "Use Tab Zoom" in Settings, Web Pages.
To my way of thinking, it seems to be back to front . When disabled, the current tab's zoom level is used for new tabs. When enabled, the 100% zoom setting is used.