I went to review a personal journal from March and get a message that it couldn’t be opened. I’ve been using LibreOffice for journals for years, and none of the older ones will open. For a few months I tried out a Chromebook then changed back to a Windows PC, transferring files from my old Windows PC. The files will still open on that one, in version 6.4.4.2.
What is the exact message, and how are you attempting to open the file? Via File | Open, double click from a file manager, from the recent documents list, something else?
It might have been Blocked by Windows as it came from another computer. Open File Explorer, navigate to the file, right-click on it, select Properties and in the tab taht says General, untick the box that says “This file came from another computer and might be blocked to help protect this computer”. Cheers, Al