Separate issue visibility?

Hello there,
we would like to separate the issue visibility between internal issues and customer-created issues. Does anyone have an idea for this ?
The only feature I found was “confidential issues”, but it doesnt exactly match our needs.

One idea was to mirror two gitlab-repositories, one containing customer-issues and the other one containing our issues. But repo-mirroring doesnt seem to work from gitlab-repo to gitlab-repo ?!

But maybe I´m just searching in the wrong direction. Could anyone give me a hint ?