I feel your pain, but at least I was not alone. Biggest headache for me was I have a few hundred tabs open over dozens of workspaces. Took a while to rebuild\reimport.
My only fix was to delete all traces of all extensions and extension settings. All of the folders with “Extension” in the name that were in my profile. Only then could I restart Vivaldi and cleanly rebuild. And then I had to reimport an old sessions from the day before.
Thankfully I had backups of all the data from all of those various extensions.
I did not delete my profile.
I now have all extensions working again - including ViolentMonkey. Though I slowly added extensions one by one until things settles happy.
But never have I had such pain of a browser just not restarting at ALL like that before. (And Sod’s Law says it happened on a day my backup server was offline…)