Evolution (3.34.1 from Flathub) running as a Flatpak cannot print emails due to bug https://gitlab.gnome.org/GNOME/evolution/issues/515 and https://bugs.webkit.org/show_bug.cgi?id=192748 This bug effects only emails - calendar, tasks etc, print ok.
However you can do a print-to-file, but the output seems to be placed into the containers file-system, so it cannot be accessed. For me a workaround to this was to run Evolution with access to the users /home file system enabled:
flatpak run --filesystem=home org.gnome.Evolution
I was wondering if this shouldn’t be a usual sandbox permission for Evolution or if there is a security reason it is not enabled?