GTK client 8.0 does not launch LibO for reports

Hello everybody,
on my ubuntu 26 machine, I have installed:

$ flatpak list | grep -i tryton
Tryton 7.0	org.tryton.Tryton-70	7.0.40	stable	system
Tryton 8.0	org.tryton.Tryton-80	8.0.5	stable	system

With the 8.0 flatpak client, no odt report will be opened, no invoice, pick list, sale, whatever. No problem with the 7.0 flatpak, and no problem with the 8.0 pip client.
I can deal with the pip client, so no problem for me - but maybe somebody is interested.

EG

It is probably because you do not have a proper configuration for the platform version.

I could not find out how to solve this problem. Till now, all properties of any flatpak app I installed have completely been handled by the OS, resp. the flatpak itself.
What needs to be done, and is there some place where required procedures are described?

Thanks a lot

This is Flatpak/Gtk topic. The client is calling Gio.AppInfo.launch_default_for_uri to open the file.