Since this is abandoned, I’m asking eveyone who comes here, what they use instead…
It has to open PDF, DjVu, EPUP, XPS, and must not be ”minimalistic“ or in other ways over-”simplified“. And preferably open source, but in any case not nagware/adware/spyware or other commercial malware.
Here’s the obligatory AlternativeTo.net link.
Seems like Librera Reader has the same security holes. And Shelf isn’t in F-Droid.