You can install gzdoom and freedoom off the AUR and run several mods and third party wads with it (most aren't compatible with freedoom, but some are), in like

You can install gzdoom and freedoom off the AUR and run several mods and third party wads with it (most aren't compatible with freedoom, but some are), in like three commands, and it adds the file association for wads to gzdoom so if you open any wad in a file manager it runs in gzdoom. That setup works out of the box without any copy / paste of files anywhere.