Do you mean fullscreen, or maximized window? Note that this likely not specific to libreoffice. The application just happens to enforce a minimum window width that appears to be larger than the width of your screen when in portrait orientation. That would affects similarly other applications that enforce a minimum width for their windows.
Regardless, would you mind filing an upstream bug report at https://bugs.documentfoundation.org/enter_bug.cgi?product=LibreOffice&format=guided, to get upstream's take on the problem? Please share the link to that bug report here. Thanks! ** Changed in: libreoffice (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to libreoffice in Ubuntu. https://bugs.launchpad.net/bugs/1806292 Title: Working not possible in portrait mode Status in libreoffice package in Ubuntu: Incomplete Bug description: As described above. I've turned my screen around to work in portrait mode. Sadly LibreOffice came out of the full screen mode. Full screen mode seems not to be possible on portrait mode. The window didn't fit into the screen and therefore it isn't possible to work with LibreOffice in portrait mode. I'll attach a screenshot to clarify what I mean. ProblemType: Bug DistroRelease: Ubuntu 18.10 Package: libreoffice-writer 1:6.1.2-0ubuntu1.1 ProcVersionSignature: Ubuntu 4.18.0-11.12-generic 4.18.12 Uname: Linux 4.18.0-11-generic x86_64 ApportVersion: 2.20.10-0ubuntu13.1 Architecture: amd64 CurrentDesktop: ubuntu:GNOME Date: Sun Dec 2 22:52:10 2018 InstallationDate: Installed on 2018-11-30 (2 days ago) InstallationMedia: Ubuntu 18.10 "Cosmic Cuttlefish" - Release amd64 (20181017.3) ProcEnviron: TERM=xterm-256color PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=de_DE.UTF-8 SHELL=/bin/bash SourcePackage: libreoffice UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/libreoffice/+bug/1806292/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp