lubuntu sets qt5 as default UI backend for libreoffice, breaking printing

[QuImUfu]

/etc/xdg/xdg-Lubuntu/lxqt/session.conf sets SAL_USE_VCLPLUGIN=qt5 as environment variable, causing the bug described here (https://ask.libreoffice.org/en/question/252543/writer-export-to-pdf-has-no-text/) to appear, i.e. printing or exporting to PDF causes all text to vanish from documents.
On Lubuntu 20.04.1 LTS

[Beluga (buovjaga)]

Lubuntu needs to switch away from defaulting to qt5. According to LibreOffice developers, "using plain "qt5" VCL plugin in production is something we don't recommend". Even the readme says it's "under construction": https://docs.libreoffice.org/vcl.html

[Michael Weghorn (michaelweghorn)]

For some more background, see also https://github.com/lxqt/lxqt-session/pull/278 (which is the pull request where it was discussed whether or not to set SAL_USE_VCLPLUGIN=qt5 in upstream LxQt).

Short summary:
SAL_USE_VCLPLUGIN=qt5 by itself isn't tested upstream and definitely experimental. If you really want to use it, set SAL_VCL_QT5_USE_CAIRO=1 in addition, which *should* probably work pretty well (mostly like the "kf5" plugin, which is used by default on Plasma and LXQt according to LibreOffice's default selection mechanism), but is also not tested/used by upstream.