The subscription version of NaturalReader is pretty good. The AI voices are quite natural in it compared to the free version. Even the free version voices are decent. The mobile app is for iOS, so if you have a retired iPhone around after having switched your main phone to pixel/graphene, you can use it on wifi. Or use the web interface with your browser on a Linux laptop and pipe it to a Bluetooth speaker. You can import any text or pdf into it. Webpages, pdf books, OCR text, etc. and set custom reading speed. And it has captions so you can read and listen at the same time to enhance retention. It has really increased the number of books I read in a year.