Currently I’m using booky mcbookface but the app is really lacking and the scrolling is not smooth.
Edit: I came across Lithium and Readera which both don’t seem to collect much information compared to other apps. Not sure if they’re open source though.
My overall favourite app replacing the Kindle app. It is available on almost all platforms. Fully open source and free.
https://readest.com/
It’s tts is broken last time I used it. It only let me use edge tts and not my system default one.