You realize that I was referring to fanfiction, right? That's material that's either in print form (for stuff originally published up until the late '90s) or on a website (for stuff published after the '90s or earlier material that's been uploaded). It's customary to tag such stories in various ways to let people know that if they don't like same-sex couples, they should avoid them, or if they don't like heterosexual couples they should avoid those (this is actually a point of contention in Harry Potter fandom as there are three general ideas about Sirius Black and Remus Lupin - either they're a couple, aka Wolfstar, or they're not, or the reader doesn't care and will read any story about them as long as it's handled well). There are other reasons to tag a story, including if any characters have been genderswapped or the ethnicity has been changed.Unfortunately for you, it's not that obvious. If it was, it wouldn't be the case that virtually every adaptation today feature significant (at least from your perspective) changes, for one reason or another. And they won't be tagged or anything, and you probably won't get alternative versions that are 100% faithful.
You can either reason it out and accept them or continue to be upset and rail at them perpetually.
Again, with Harry Potter, there are some stories that feature James Potter as having a white father and Indian mother. I have NO idea where that comes from, as it's not in the novels or the movies, and only appears in Marauders-era stories. How those authors can square this with the descriptions of Harry and his parents in the novels and what we see in the movies, I can't fathom.