I know the Flatpak version is marked as 'unsupported', but I'm just filing this query for consideration. Flatpaks are run in 'sand boxes' and so have limited access to other installs within the system. This means that Flatpaks cannot 'see' other Flatpak applications, and therefore cannot run LibreOffice Flatpak to display presentations. However, other Flatpaks get around this by allowing a user to identify applications to run. Could you look at how to allow Flatpaks to display Presentations via LibreOffice and videos via (e.g. VLC). Linux distributions are gradually moving to containerised applications, and I run a Fedora 'Atomic' desktop which is containerised throughout (including the OS); people are moving to this more secure way of running applications and so addressing this needs will have real long-term benefits.
Huge thanks!