I eventually also got it to work.
I tried uninstalling, which always led to the same error, but in fact files and/or registry settings had been changed/deleted.
It needed a reboot of the system, but after that I was able to re-install Opera and everything works properly again

Trying to uninstall leads to the same error.
Trying to re-install / over-install the latest and greatest, downloaded from the website, starts but eventually runs into the same error

Completely stuck

Same here !