Epson ImageScan (utsushi) needs /etc config to work

The application installs, but can not be used. For use of this application, the user needs to edit /etc/imagescan/imagescan.conf to provide network details of the scanner. However, there is no apparent way to set this file up in such a way that the flatpak application would be able to see it.

You should file an issue it is more likely the flatpak maintainer pay attention there.