I just had the exact same issue as you are experiencing! Simply go into /usr/share/xfce4/helpers and delete the icon labeled “vivaldi”. Then, attempt to update again. After updating, you should notice that it has replaced the former vivaldi icon with, wait for it, another identical one! This confuses the computer, so deleting the old one before updating is sadly necessary. Afterwards however, it is back where it should be.
Hope this helps!
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