Starting on 18th May 2021 all ebook listings will be disapproved. Source: https://support.google.com/merchants/answer/10524536
Remove all ebooks from your data feed listing to prepare Google’s Policy changes.
This policy applies to all Google Merchant Center channels except for Free Listings. This means you can continue to receive free clicks for eBooks, just not for Shopping Ads, Display, Buy On Google, Local Ads.
Google has for a while not been great with selling digital content on Google Shopping Ads. There have been issues with verifying the content sold is genuine.
That in combination that Google could not offer a great user experience. They simply decided not to allow these products all to gather.
If you are selling hard cover prints, but are flagged for eBooks, then make sure that you have done the following.
Start selling hard cover prints or sell your ebooks on a different marketplace.