Hi,
Thanks for your contribution.
Does this actually fixes the issue? As I suppose you'll have both core-js 2 and 3 as dependency but they can't work concurrently so I'm not sure to see how that would fix it?
If you check the simplebar package, there is the corejs 3 configuration in place there. Maybe there should just be the same thing in the vue package?

Yeah. It fixed this issue for me.
Right now issue is that simplebar-vue does not have core-js package specified as dependency at all. It just uses hoisted package version, so if app has core-js@3 in its package.json it will try to use that. It does not use core-js@3 dependency from simplebar package. And even if it did it would not work because current babel config for simplebar-vue generates core-js imports using version 2 format.
Best solution would, probably, be to update vue related dependencies (babel preset) for simplebar-vue and switch to core-js@3.
I can update this pull-request to include that.

Just checked vue packages and @vue/babel-preset-app@3.8.0 is not updated to core@3 yet. And version 4, where it is updated, is in alpha.

I have removed @vue/cli-service and related packages - they were used mostly for tests. Instead I have added vue-jest and used jest directly for tests. Additionally I have removed @vue/babel-preset-app and used just @babel/preset-env. This allowed me to switch to core-js@3.
Tests are passing, but I will test tomorrow on my project for both core-js@2 and core-js@3
Another benefit of these changes are 3.5k lines removed from yarn.lock 🙂

Just tested and it worked in both cases: when app is targeting core-js@2 and when core-js@3