Dark theme not working under LXQt

[Chirunos]

Official flatpak, org.gtk.Gtk3theme.Breeze-Dark installed and GTK_THEME=Breeze-Dark set.
neofetch output:

lt@gnu0:~> neowofetch
                 `-++:`                    lt@gnu0 
               ./oooooo/-                  ------- 
            `:oooooooooooo:.               OS: openSUSE Leap 15.6 x86_64 
          -+oooooooooooooooo+-`            Kernel: 6.4.0-150600.23.22-default 
       ./oooooooooooooooooooooo/-          Uptime: 8 hours, 11 mins 
      :oooooooooooooooooooooooooo:         Packages: 1855 (rpm), 34 (brew), 3 (steam), 2 (guix-user), 36 (flatpak-system), 12 (snap) 
    `  `-+oooooooooooooooooooo/-   `       Shell: bash 4.4.23 
 `:oo/-   .:ooooooooooooooo+:`  `-+oo/.    Resolution: 1366x768 @ 60.00Hz 
`/oooooo:.   -/oooooooooo/.   ./oooooo/.   DE: LXQt 1.4.0 (x11)
  `:+ooooo+-`  `:+oooo+-   `:oooooo+:`     WM: KWin
     .:oooooo/.   .::`   -+oooooo/.        Theme: Breeze [Qt], Breeze-Dark [GTK2/3]
        -/oooooo:.    ./oooooo+-           Icons: breeze-dark [Qt/GTK2/3]
          `:+ooooo+-:+oooooo:`             Cursor: breeze-dark [Qt], breeze_cursors [GTK2/3]
             ./oooooooooo/.                Terminal: gnome-terminal
                -/oooo+:`                  CPU: Pentium T4500 (2) @ 2.3GHz
                  `:/.                     GPU: Intel Mobile 4 Series Chipset
                                           Memory: 1.60 GiB / 2.87 GiB (55%)
                                           Network: Wifi                                          

[OvercookedBeef]

It works for me

[Chirunos]

Looked at mainwindow.ui again and only now I noticed the dark theme, turning this into a bug report instead.