There are multiple options both stable and daily:
Note 1: UNINSTALL duplicity first if it was installed from a different source.. This is due to divergent install locations, especially between repository installs and the other forms.
Note 2: Launchpad PPAs contain builds for Bionic 18.04, Eoan 19.10, Focal 20.04, and Hirsute 20.10. Xenial 16.04 works with Snap and Pip installs, but cannot be built under Launchpad PPAs at the moment.