get-all-items-all-post-types.js

// Helper: wait for all records of a given post type.
const getTypes = async ( types ) => {
	return await Promise.all(
		types.map(
			( type ) =>
				new Promise( ( resolve ) => {
					const unsub = wp.data.subscribe( () => {
						const items = wp.data
							.select( 'core' )
							.getEntityRecords( 'postType', type );

						if ( items ) {
							unsub();
							resolve( { type, items } );
						}
					} );
				} )
		)
	);
};

// Helper: wait until all post types are available.
const getAllPostTypes = () => {
	return new Promise( ( resolve ) => {
		const unsub = wp.data.subscribe( () => {
			const postTypes = wp.data
				.select( 'core' )
				.getEntityRecords( 'root', 'postType' );

			if ( postTypes ) {
				unsub();
				resolve( postTypes.map( ( { slug } ) => slug ) );
			}
		} );
	} );
};

// Combine both: first get all post types, then their entities.
const getAllTypesWithEntities = async () => {
	const types = await getAllPostTypes();
	const results = await getTypes( types );

	results.forEach( ( { type, items } ) => {
		console.log( `Fetched ${ items.length } records for ${ type }` );
	} );
};

// Run it
getAllTypesWithEntities();

get-all-items-selected-post-types.js

const getTypes = async (types) => await Promise.all(types.map(type => 
  new Promise(resolve => {
    const unsub = wp.data.subscribe(() => {
      const items = wp.data.select('core').getEntityRecords('postType', type);
      items && (unsub(), resolve({ type, items }));
    });
  })
));

// Use it
(await getTypes(['post','page'])).forEach(console.log);