It is recommended to use the packaged version of Scribus, not a Snap.
(maybe sudo) apt install libreoffice-script-provider-python python3-icalendar python3-recurring-ical-events python3-urllib3 python3-iniparse python3-markdown
If python3-recurring-ical-events is not found in APT, you'll need to install python3-pip, and then: pip install recurring-ical-events