CommonJS or AMD dependencies can cause optimization bailouts warning.

[cami-dev]

I keep getting this warning when I run our angular library in an angular application. The library itself has ckeditor as peerdependency and has compenents that uses ckeditor, so the app installs ckeditor in their own package.json. I'm trying to understand why this warning occurs and what I understand it's saying that ckeditor is not built on ECMAScript modules?

Warning: libname.mjs depends on '@ckeditor/ckeditor5-build-classic'. CommonJS or AMD dependencies can cause optimization bailouts. For more info see: https://angular.io/guide/build#configuring-commonjs-dependencies

I can silence this by adding the following to the angular.json, but should this really happen? As I understood ckeditor is using ESmodules, or is it not?
"allowedCommonJsDependencies": [
"ckeditor"
]