Reintroduce Dark Theme Toggle
I don't want to ask you to re-include things for the sake of re-including things, but I think it will legitimately simplify GTK themes both in and outside GNOME.
When you set the gtk theme to a dark theme properly through settings.ini (e.g. gtk-application-prefer-dark-theme=1), applications like Firefox can ignore the overriding dark theme .css file and use the default .css file instead, which will save a lot of users a headache because the dark theme often breaks entry boxes on web browsers, which can force users to create userChrome.css files they don't actually need. If you however use something like SOMETHEMEHERE-Dark that are often packaged together with most themes these days from the theme dropdown, the dark theme is the default .css, so it will not allow applications like Firefox that should ignore the dark theme override to use a default .css file that is better suited for displaying on web browsers.
The lack of this feature encourages those THEME-dark variations that just don't work properly. I wouldn't even say GNOME is solely guilty for this, KDE for example has a separate BREEZE-DARK gtk theme when they could simply use the gtk-application-prefer-dark-theme=1 line instead. Anything that would discourage this practice is preferred, and since GNOME develops GTK, change should start from the top and trickle back down to the other desktops.
It doesn't exactly have to be the toggle button, I just want this feature to be used by Gnome-tweaks again. At the very least, would it be possible for tweaks to not override gtk-application-prefer-dark-theme? it may seem like people don't switch themes much but I do swap to adawaita/stock icons to work on GTK applications and then swap back to what I prefer when I'm simply using my desktop.