At the moment they don't have an official support for typescript while using CKEditor5, which is really bad in my opnion. But I know this is an old issue, you can check it more here:
Whether you're facing some errors try creating a file ckeditor.d.ts and adding this:
declare module '@ckeditor/ckeditor5-react' {
import ClassicEditor from '@ckeditor/ckeditor5-build-classic';
import Event from '@ckeditor/ckeditor5-utils/src/eventinfo'
import { EditorConfig } from '@ckeditor/ckeditor5-core/src/editor/editorconfig'
import * as React from 'react';
const CKEditor: React.FunctionComponent<{
disabled?: boolean;
editor: typeof ClassicEditor;
data?: string;
id?: string;
config?: EditorConfig;
onReady?: (editor: ClassicEditor) => void;
onChange?: (event: Event, editor: ClassicEditor) => void;
onBlur?: (event: Event, editor: ClassicEditor) => void;
onFocus?: (event: Event, editor: ClassicEditor) => void;
onError?: (event: Event, editor: ClassicEditor) => void;
}>
export { CKEditor };
}