First edit the /etc/apt/sources.list file and add the following Mirrors. Do this only if your distribution does not have Fluxbox in its package.
deb https://deb.parrot.sh/parrot lts main contrib non-free
deb https://deb.parrot.sh/parrot lts-updates main contrib non-free
deb https://deb.parrot.sh/parrot lts-backports main contrib non-free
deb https://deb.parrot.sh/parrot lts-security main contrib non-free
You can edit the autoconf.sh file before running it and comment out lines 3 and 4 if you did not need to import the mirrors to install Fluxbox, Xorg and Rxvt-unicode, you can also comment out the last line if you want a manual reboot.
git clone https://github.com/kr4k3nb1t3/Auto-Blackarch-WM-Theme-For-Deb.git
cd Auto-Blackarch-WM-Theme-For-Deb
chmod +x autoconf.sh
./autoconf.sh
git clone https://github.com/trizen/fbmenugen && cd fbmenugen
sudo apt install -y libgtk3-perl
sudo cpan Linux::DesktopFiles && sudo cpan File::DesktopEntry
chmod +x fbmenugen
sudo cp -r schema.pl /home/x/.config/fbmenugen/
./fbmenugen -g -i
./fbmenugen -g