Thanks @UncleSpellbinder ! This works for Timeshift as well. However, I need to explicitly set the theme to Breeze-Dark. If I set it to Breeze, it stays in light mode.
A side note…
I decided to try out GNOME this weekend and I got nothing more than a serious headache and conviction that GNOME can only be used in a way the developers intended it to be.
If you want your apps to look uniform in there, well… good luck.
And that is why I switched from GNOME to KDE some time ago. GNOME really is more like MAC in the sense that it has a very opinionated view of the world.
It’s not like you can easily setup a tiling window manager as a desktop environment if you want to use it as that, now with Hyprland and Niri with QuickShell project it’s gotten a lot easier to use it as a desktop environment.
At least for me the beauty of running i3 is that it encouraged me to find text-based apps (with Vim-oriented keyboard controls) to get most things done.
Those occasions for which that a KDE or GNOME app is needed have been whittled down considerably over the years. As another i3 user, I’d encourage you to maximize those opportunities to simplify things.