I downloaded the newest 2.2 and in preferences i saw a "Prefer Dark theme" option but enabling it does nothing, even after restarting the client. Windows 10.

... Changes: [GtkUI] Reword preferences to prefer dark theme [WebUI] Refactor changing theme [GtkUI] Add a way to change themes ... retry unhandled alerts [Core] Call wait_for_alert in a thread [CI] Fix windows packaging build [UI][Common] Add daemon version check [Core] Support ...

With the above help from mhertz I could made a simple python app.
It can change Deluge's theme to dark or custom one (with color picker).
Here: https://github.com/delington/Deluge-theme-changer

If you want to use dark and custom themes for Deluge 2.0 on Windows, check out:

https://github.com/delington/Deluge-theme-changer

... not by me atleast, as said i'm honestly avoiding messing with these themes. For people wanting a black theme, id just recommend the builtin adwaita-dark, ... old version of Deluge. I've just installed the latest version 2.1.1 on windows 11, and I'd like to know what's the easiest way to get a dark ...

Agreed, but meanwhile it's just a text file with 2 lines needing added, as dark theme already included in gtk3 dll/so. Maybe also a dir, don't know if already there, cannot remember from top of head(I believe needs added a gtk-3-0 dir to \share(for settings.ini), ...

... adding in font-size etc, as statusbar property in standard adwaita gtk3 theme, which I added externally and defined for usage, and I could control ... in quick testing. statusbar { font-size: 16pt; } Also, there are in the windows installer, included a few gtk-builder ui files, as fails freezing, ...

... in contrary to deluge v1.x. I'm unsure about if can change this from a theme through CSS, but honestly doubt it, as directly hardcoded, and I doubt ... in full, but though very well could be wrong. I see you're using windows, meaning this cannot just be edited in the python source-code, but ...

... having classic mode enabled in win7 then you need select other deluge theme than the default during install, as else the deluge GTKUI is borked ... a disc from said drive, then rigtclick drive and select eject in windows explorer(I know empty but regardless), so windows shows error as ...

... this issue and solution with anyone who might encounter it. I use Windows 11 and I've been trying to set up the basic dark mode for Deluge, ... (utf8) and restarting the program, it succesfully changed to the dark theme. Very specific for my case, the debug executable was extremely useful ...