For the legal sticklers among you that claim mods aren’t inherently illegal. They are, for two reasons.
Here’s a law review journal’s thoughts on it.
First reason
Courts have concluded that game mods are a derivative work and therefore the ownership lies with gaming companies having the requisite copyrights. Game mods therefore have not been viewed by courts as a value-add to the original work of the gaming companies, but rather as an infringement of their copyrighted work.
Second Reason
However, courts in the United States have held that modders are restricted from claiming copyright over their creation, even after putting in hard work for creating such a mod. Thus, modders cannot assert ownership over their work and cannot legally profit without infringing the game owner’s copyright.
Modders who send DMCA copyright strikes to Discord, Kemono, Google, Mega, or any other platform for sharing their mods are most likely acting unlawfully, as they cannot claim copyright over their creations under US law.