Hi,
The installation process for Duplicati is very straightforward. Download the MacOS X version from:
https://www.duplicati.com/download
Open the DMG file (double click it in your Downloads folder) and drag the Duplicati icon on the Applications icon. Once copied, just double click launch it within your Applications folder.
Sometimes (depending on what other things you have already installed), you’ll be prompted to install “Mono”. This can be found here:
https://www.mono-project.com/download/stable/
HOWEVER
On recent versions of MacOS there is a bug which stops Duplicati starting up properly and it’s quite fiddly to workaround:
https://forum.duplicati.com/t/duplicati-not-starting-on-macos-monterey-12-3-on-m1/14096/9