If your Vivaldi crashes on startup look here
EDIT: There is a beta fix provided here that should fix your problem: https://vivaldi.com/blog/snapshots/the-start-of-1-13-stablization-vivaldi-browser-snapshot-1-13-998-3/
A number of users are having this issue after the latest update. If you don't care about maintaining your Vivaldi configuration type windows+R and then %appdata%, path to your /local/Vivaldi folder and delete everything inside. Reinstall Vivaldi and it should start up again.
If you want to save your config and wait for an update, backup the files inside /local/Vivaldi first before deleting them.
Have a nice evening
For problems with crash on 1.12.955.42 Stable go to https://forum.vivaldi.net/post/168634