Well, you should have it, since that's why you get the error, the .png files and the .mcmeta files since the .mcmeta files are for animation if I'm not mistaken.
This is what the .mcmeta have.
So basically, I'm fairly new to linux, and I have no idea how to install forge. I run Linux Debian 10 (Buster), and I have Java edition Minecraft. I've installed the .jar file, but I don't know where to go from there.