You could give ReLaunchX launcher a try. Its built for ereaders, and has many customization features.
https://www.mobileread.com/forums/sh...d.php?t=284418
For your case, it displays files in a folder in a list view, which is pretty condensed. around 20 files per page in 2 columns in my 6inch tab.
I used it for a few months, but then switched back to the default launcher.
There is a library view and a launcher mode. Best results are when you use it as a launcher.
The pdf reader Librera is also e-ink compatible and features a library view of its own. It is decent for opening pdfs, but has problems with some complex files.
https://play.google.com/store/apps/d...k.reader&hl=en
For floating back button and previous app switcher, I use this
https://play.google.com/store/apps/d...syswitch&hl=en