There is a kindle app for the iPad

There is an opinion that a new Kindle will be announced soon.

To be specific, I want an app on Android which can save bookmarks from devices to devices, and can import external files🤔

I like the eReader Prestigio myself

https://play.google.com/store/apps/details?id=com.prestigio.ereader

#bookstr

I got a kobo libre color recently. It's good for comics too. Pdfs are slow but there are pc apps to convert them to epub if drm free

Boox Palma

Runs with Android, so all the reader apps work...