when you are able to start up Minecraft in Forge you should be able to go to settings and select resource packs and load the file into there.
Mine only worked when I unzipped the file then dragged it into list but that could have just been a problem for me.
This is not a mod, but a resource pack, you just need to install optifine (the person above sent the instructions), then unzip the archive into a resourcepacks folder, and then select the resource pack in the game settings
Can you make this for something that isnt optifine? Maybe something like Rubidium or other alternatives to optifine? It being stuck to optifine basically means a few very essential mods for playing fatcraft and tons of others non related cant be used with this at the same time.
Many mods also just arent up to date as 1.21.4, many are still on 1.21.1. Im still stuck on 1.16.5 for example.
If you have the correct version of forge installed and optifine or the alternative mods listed above, all you need to do to get this working is put it in the resource pack folder and then select it in game. Make sure you unpack it, dont just stick the zip file in there.
I started it up on the most current version, like the sounds work for it but the models do not. I tried using Optifine with the resourcepack which gave me error code -1
I tried that as well, which the good news is it loaded up, however that’s how I figured out the models don’t work but the audio does.(I picked the gassy mobs so)