I use both CDK and NG-Bootstrap in my side-project.
While I was building a modal within which an interaction happens for which I wanted to use CDK-LiveAnnouncer I noticed an interesting interaction:

Ng-Bootstrap, when opening a modal, appears to be applying aria-hidden="true" to ever direct child of the body-tag as long as it's not a script-tag. This includes the aria-live region that i.e. cdk-live-announcer uses to announce its code.

This of course makes it effectively impossible to announce anything with LiveAnnouncer while an Ng-Bootstrap modal is open.

I would therefore propose that when fetching all elements to apply aria-hidden to when a modal opens, that elements that contain the aria-live attribute should be excluded from that step.

Minimal reproduction to demonstrate the issue: https://stackblitz.com/edit/stackblitz-starters-dpmg6qns?file=src%2Fdialog.ts