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Feel free to keep the gtk2 version alive in AUR, gtk2 has been EOL for a bit over 4 years so I won't bring the gtk2 version back. https://blog.gtk.org/2020/12/16/gtk-4-0/
I personally have used the gtk2 version, qt5 and qt6 version and doublecmd always looked the same for me. But ok that might not be the case for you so no arguing there.