@tigercat
I am sorry, you have to search yourself, no time for this.
Install an old version of Vivaldi as standalone install and copy the icons, the path on Windows is:
Application/6.0.2979.25/resources/vivaldi/resources/
Don´t install older version over the new one.
https://help.vivaldi.com/desktop/install-update/standalone-version-of-vivaldi/