I feel stupid for asking this, but I have been bashing my head against youtube and google to figure this out, but where exactly do we put the mod in the folders? Or does it not work for the steam released version of Ultimate Doom?
it does not, its a mod for the Zandronum port!
you need to install it here: https://zandronum.com/download
and then put the wad files for doom inside the directory where you store the port contents in.
and once youve done that, you can just drag the pk3 to the zandronum.exe file and play!