I tried launching hyprland-share-picker with different QT_QPA_PLATFORMTHEME variables and setting it to gtk3 works, but when the window loses focus it looks bad, so I think the qt6ct style is not working for some reason.

Here is my home.nix:

{
  ...
  gtk = {  
    enable = true;  
    theme.name = "Catppuccin-Mocha-Standard-Blue-Dark";  
    cursorTheme.name = "Adwaita";  
    cursorTheme.size = 24;  
    iconTheme.name = "Tela-circle-dracula-dark";  
    font.name = "Inter Nerd Font";  
    font.size = 12;  
  };  
  home.pointerCursor = {  
    gtk.enable = true;  
    package = pkgs.gnome-themes-extra;  
    name = "Adwaita";  
    size = 24;  
  };  
  qt = {  
    enable = true;  
    platformTheme = "qtct";  
  };
  ...
}