This is one of the best articles on illegal mods.

https://kblroche.com/thinking-before-modding-players-dont-own-what-they-make-2656426399.html

A quote from the article,
"I’m a modder! What does this mean for me?

Well, the*harsh answer is:*either*don’t mod at all, mod only for works where the rights-holder has condoned the practice, or keep your mod private instead of releasing it to the public (which is still infringement, but without anyone noticing it). If a rights-holder does not like your mod, then they can and will strike your mod down (via a cease and desist letter and a DMCA Take Down Notice most likely). Once that happens, there is not really anything you can do. If you want to release a mod of a game you do not own any copyright in, your best bet is to*ask the rights-holder for permission."

It is very clear from this International Law Firm Article that unwanted mods, whether they are provided for \\'free\\' or paid or held privately or publicly, the unwanted mods are illegal and copyright infringement.