Did you copy the extension.cfg from the zip-file and overwrite the file that was on your device?
If so, that explains why you can't open books.
Edit the file and make sure you don't have only cr3-pb as alternative. Also put eink-reader.app first.
Like this:
epub:@EPUB_file:1:eink-reader.app,AdobeViewer.app,cr3-pb.app:ICON_EPUB
(+ for the other formats)
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