Yes, it's working with the "workaround".
I started the Enpass desktop client anyway at boot, so it's no problem for me. But it should working too, if you first starting Vivaldi (with installed Enpass extension) and then starting the Enpass desktop client, that's why I have open a bug-report in Vivaldi's bug-tracker.
Here is the link for our discussion in Vivaldi's forum: https://vivaldi.net/en-US/forum/3rd-party-extensions/10885-enpass-extension-is-not-working