Libreoffice cant read or write files with cyrillic (russian) names or placed in “cyrillic” folders.
Unfortunally, user folder “Documents” folder named in russian at last, so libreoffice cant work at all…
This normally means that LibreOffice or its runtime is installed without the ru locales. Is an update for LibreOffice available in the app center? If so, try installing it.
People fixed this bug on early LO releases by symlinking US locale to RU. There are US locale hard coded in OPEN/SAVE dialog somethere. Root partition under Endless mounted r\o so we have nothing to simlynk there. And APP packet hard compiled too.
Under (current) Debian distro there is no this bug “out of the box”. Launch. Work.