Tried which? What failed?
FWIW unzip of 2.0.8.1, install of mono-complete, and mono ./Duplicati.Server.exe works for me, however I’m on Ubuntu 24.04. Because it’s not a TrayIcon, browse to localhost:8200 by hand.
TrayIcon (unlike Server) does not start, presumably due to OS removing graphics dependencies.
mono ./Duplicati.GUI.TrayIcon.exe
Unexpected error: System.TypeLoadException: Could not load type of field 'Duplicati.GUI.TrayIcon.GtkRunner:m_trayIcon' (1) due to: Could not load file or assembly 'gtk-sharp, Version=2.12.0.0, Culture=neutral, PublicKeyToken=35e10195dab3c99f' or one of its dependencies.
at Duplicati.GUI.TrayIcon.Program.RunTrayIcon (System.String toolkit) [0x00027] in <3ea059db9f9241b999c39793a8f6f091>:0
at Duplicati.GUI.TrayIcon.Program.StartTray (System.String[] _args, System.Collections.Generic.Dictionary`2[TKey,TValue] options, System.String toolkit, Duplicati.GUI.TrayIcon.HostedInstanceKeeper hosted, System.String password, System.Boolean saltedpassword) [0x00066] in <3ea059db9f9241b999c39793a8f6f091>:0
My 2.0.8.1 dependency lack is like yours on the appindicator side, plus also has a GTK problem:
The following packages have unmet dependencies:
duplicati : Depends: libappindicator0.1-cil but it is not installable or
libappindicator3-0.1-cil but it is not installable or
libayatana-appindicator1 but it is not installable
Depends: gtk-sharp2 but it is not installable
but (at least so far) the .zip install works. If yours did not, please give some information on that.