There are multiple options both stable and latest:
Stable snap builds - “sudo snap install duplicity —classic"
Latest snap builds - “sudo snap install duplicity —classic —edge"
Stable pip3 builds - “sudo pip3 install duplicity"
Latest pip3 builds - “sudo pip3 install --pre duplicity"
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, Hirsute 20.10 and Impish 21.04.
Note 3: Xenial 16.04 works with Snap and Pip installs, but cannot be built under Launchpad PPAs at the moment.
...Thanks,
...Ken