> - I don't use the Books app, I use the Amazon Kindle app

Amazon Kindle Direct Publishing offers 2 options: 35% royalty and 70% royalty.

https://kdp.amazon.com/en_US/help/topic/G200644210

You can choose between two royalty options for each of your eBooks: the 35% royalty option and the 70% royalty option.

-If you select the 35% royalty option, your royalty will be 35% of your list price without VAT for each unit sold.

-If you select the 70% royalty option, your royalty will be 70% of your list price without VAT, less delivery costs (average delivery costs are $0.06 per unit sold, and vary by file size), for each eligible book sold to customers in the 70% territories, and 35% of the list price without VAT for each unit sold to customers residing outside the 70% territories.