This class is visible to consumers via SomeModule -> SomeComponent, but is not exported from the top-level library entrypoint

This error happens if any component is exported in NgModuleand not included in your public_api.ts, angular 9 will through error now.

This error was not coming in angular 8 but after upgrading to angular 9 it started showing.

If you exported any service, module or component, etc in NgModule make sure to include them in public_api.ts or else angular 9 will throw error now.

Fix: add your component to the public_api.ts

export * from './lib/components/some-me/some-me.component';