It's always safer to create all the assets, music, etc. for your games, or to use copyleft resources (things in the public domain, Creative Commons, GPLs, etc.). So, you're doing the right thing. In fact, I do the same, so high five! ✋ haha.
Now I'm going to explain what I understand about this legal issue. If I'm wrong, please let me know. Only the owner of registered (i.e., copyrighted) material, or a representative appointed by them, can file a complaint. The platform, whether it's Steam, Itch.io, or any other, can't prohibit you from publishing a game or sue you in any way for using copyrighted material because it can't know if the original owner gave their consent or not. You could be making a fangame with Resident Evil characters with Capcom's approval, and Itch.io doesn't necessarily know about it. Capcom is a prime example, but there are many more content creators who publish their work after registering it (with copyright). Keeping track of everything is impossible, to say the least.
It is the owner of the copyrighted work, image, likeness, etc., who has the responsibility to sue those who violate the law.
Another point: Even though there is specific legislation to address these issues, it cannot be applied globally. While many aspects of US legislation are copied, the truth is that each country can make the changes it deems necessary. Basically, you are obligated to follow the laws of the country where you are located. Emphasis on "located"—it doesn't matter if your country of origin is different.
And if other countries have different copyright laws, well, tough luck.
While for now some patent holders, copyright holders, actors, actresses, etc., may not be bothered by the misuse or may even benefit from this illegitimate use of their IP addresses, likenesses, voices, etc. The truth is, if tomorrow it starts to hurt them (or for any other reason) and they decide to start cracking down on copyright infringers like Nintendo, they can do so (and impose hefty fines) because the law itself hasn't changed.
The limit is this: It's assumed that those who use any material (with or without copyright) understand the terms and conditions, as well as the risks of violating the law.
From what I understand, what you're doing is perfectly fine; you're playing it 100% safe. The others are in the wrong.