Anyone can write off the top of their heads, and it’s great for writers to do that in early drafts. But go back and revise for originality.
”Discount the first thing that comes to mind. And the 2nd, 3rd, 4th, 5th—get the obvious out of the way.” Emma Coats
“Dig until you hit rock. Then take out that jackhammer and go a little deeper.” ~Allison Brennan
This is one of the most important lessons you can learn as a writer. No writing will be 100% original. Everything is going to feel derivative in some way or another. Write down everything you think of. Then cross out the first few ideas. Refine them. Make them more interesting. Go with your 6th or 7th idea. It’s probably not been done before. Don’t do what’s been done, but if you have to do so, then make it your own. Write the story that only you can write.