I dont know everything i read online says its copyright infringement to create derivative works, outside of stuff like parodies, fair use and getting permission.
That's the important bit - the things you called illegal a few comments back were obvious examples of (presumptive) fair use.
More generally, whether something is copyright infringement can be vague and subjective - so the bar for going around saying "yes, that is infringement" is not "does it meet a description I read online?". The bar is: "have courts previously ruled that a very similar case was infringement?".
That's the important bit - the things you called illegal a few comments back were obvious examples of (presumptive) fair use.
More generally, whether something is copyright infringement can be vague and subjective - so the bar for going around saying "yes, that is infringement" is not "does it meet a description I read online?". The bar is: "have courts previously ruled that a very similar case was infringement?".