You're fighting a losing battle here, dude. Everything's derivative of everything else in some way. It's natural to be nervous about similarities, because you want everything to be unique to you.

But really everything lies in the execution. Just try to tell the story you want and don't get too hung up on similarities. And if you're really concerned, do a little reading on copyright law lol.

If you are trying to make something 100% original, you might end up driving yourself a little crazy.

Heck look at stuff like TV tropes. Most works have over lap.

I think it is more important to think about stuff like inspiration vs parody vs ripoff. Like, if your designs are too similar, then you might have to tweak them.

Nothing is 100% original, someone has always done something similar before. The trick is making it your own without fully stealing it. So if your spore things were 100% identical to that of Last of Us, then that could be an issue. But if they just happen to both be spore things then all it is, is a coinky dink.

On more than one occasion I've had people say something was similar to something I'd never even heard of, it was purely coincidental. Then a few years ago my friend joked with me that JK Rowling plagiarized me because I'd used the term Nomag for multiple years in a series I wrote, then Fantastic Beasts is announced with No-maj. We both used the term for the exact same thing (non-magic users) yet there is obviously no actual way that JK Rowling stole from me unless she was secretly reading Wattpad at the time Coincidences happen all the time.

The sad truth is that no matter how "original" you think you are there will be people who will say "Hey, this reminds me of..." In fact, some people would not even bother to look deep into your work and will point out some random superficial coincidences and compare you to others.

To me what matters it to make the story the best I can and that it is enjoyable.Of course if something ends up being the same as as any popular series, then rethinking and rewriting is what I would do.

Imitation is the sincerest form of flattery. I wrote some fanfiction, and then someone on Wattpad got inspired by my story and wrote this piece of original fiction and told me that my fanfiction had directly inspired the story. I absolutely love it and keep reading it even though I got kicked off Wattpad:
https://www.wattpad.com/story/202642886-the-year-package

Of course, after I got kicked off Wattpad, I simply set up shop on two new platforms. Here:

And also on Scribble Hub. If you happen to join Scribble Hub, please give me a one-star rating. Since the first three people gave my story one star without reading it, I decided to have some fun with it and enjoy having the lowest rating on Scribble Hub:

Everything has been done before.

But perhaps your particular combination of elements has never been done before.

Happens to all of us. The important thing is that the heart of your story is yours, that you write from your experience, from what really matters to you, from your emotions, and that you keep your eyes on what you want to say. The high concept is important, yes, but probably someone already said it or used it. Do not be discouraged if you find something similar to your story, if it is very similar, change some details and continue. Many will be able to tell the "what" of your story, but the heart is in the "how" you tell it. You follow your heart, and continue the great work.

It really isn't possible to create a story that hasn't been told before... as much as I hate to bring it up, but there was this dude named Joseph Campbell that wrote The Hero With A Thousand Faces and in it he defined the "Hero's Journey." He culled every story from every culture he could find and "discovered" that there was a common structure to all of them that can be applied from Jesus to Luke Skywalker.

The idea of originality comes from how you tell the story, and what you do with those "tropes" that everyone likes to sneer at. Me? I love a good trope. I also love turning tropes on their heads. Using different elements to create a story is what makes it original.

Every story is going to have a beginning, a middle, and an end. Its how you get there that makes it original to the creator.

It's not impossible, just kind of unlikely.
Try as you might but every fictional work will be inspired by something, whether it's historical, natural, fictional, or mythological, everything's been inspired by something.
It's really how you use the thing and explain it's existence that makes it original.

I don’t think it’s impossible, but most people try to draw similarities between things, as it helps them to understand. (Almost like analogies) or find familiarities because it’s easier for them to talk and relate to

But like others have said, it’s the execution that is important so I hope you’ll keep writing your story!

I've actually done some research on a very specific occurrence of this problem: elves.

We all know Tolkien's elves - well, they're actually derived from various Germanic mythologies. His elves come from the Ljósálfar, "light elves" in Norse mythology, and his dwarves come from Dökkálfar, or "dark elves." Tolkien's elves started as little fae creatures that danced on the moors, true to mythology, and changed over the years as he came across various other influences (Catholic theology, Celtic mythology, etc) into what we now think of as "elves."

The really funny thing about Tolkien's elves is he took centuries of mythos, went "I'm going to give them leaf-shaped ears and make them really pretty and graceful," and then thousands of fantasy writers just took it and went with it. And they didn't even care. And readers ate it up anyway because they loved elves.

I'm definitely rambling a little now, but I think there's a few morals we can take out of elvish history:

1. You can take a thing that's been done before - that's been around for a long time and easily modify it into something new. For my own novel, I borrowed Tolkien's elves and took them back a step - they're the alfar now, inspired by the original mythology Tolkien had taken his elves away from. They're still elves, they're still reminiscent of Tolkien's, but there's a new (or, I suppose, very old) twist to them.
2. Ideas can be combined into something new, like Tolkien combining Germanic mythology with other influences and inspirations to create a fantasy race that was entirely new.
3. If your idea seems similar to someone else's, understanding why the other creator did what they did and thinking about what you want from your own execution of the idea can lead to something entirely new.

Also, as others have said, everything's been done! Just roll with your idea and have fun with it

If I really like an idea, I take it but mix it with something else i really like, and I give it its own little themes and designs. That's how I do original stuff.

I have this problem all the time... I would stress about it constantly to the point I would just delete whole species or characters and then stories, but then I realized that I should hold myself back by those rude 2% who are always "that looks like A from ABCD" (especial because A often looks like D and G). Being 100% original was never a thing, not even back in the stone age with those cavemen drawing animals they saw every day, even great artists took inspiration from something from time to time, so don't worry about it.

Don't become fixated on this need to be original. You'll end up tossing away ideas you love and want to explore just because they've been done hundreds of times before. Instead make unoriginal ideas your own. Take elements of stories you like (like those mushroom zombies) and give them a fresh perspective. Twist and turn them inside out if you have to. That's how you create something new.

Some of the best writers and artists out there have done just that, and even admit it! Even the lamest and most overused ideas can become interesting if there's thought and passion behind them.

I think we're mixing two ideas again.
There's a difference between being "original" and the first to do something.
So when someone quips that "Everything has been done before" that doesn't apply to being original.

The term original is reserved for the thing that is being copied as in the Originator. Origin. The start...implies there is something after...
There is not an original without a copy.

So this means there are a million ways to be original (or have an original take) with something that has been done before.
As an artist it's your job to know your medium(s).

If your thing is to make comics, you should know more about them (and [have] read more) than the average fan.
And what is original (or rarely done) to YOU should be more so to them.

That's one of the buffers against accidentally copying (having similar) ideas and stories and lore and, and...to other works.

The "Origin" of your story may be familiar or has a common setting or tone or set or plot, but over time, you're supposed to express the YOU and that's where the originality is supposed to kick in.

You make a new and unique dish with common ingredients.
This is also about the artist' journey which (broadly) goes from copying to doing stuff that hasn't been done before or simply isn't being done so you still get the credit of being original (and sometimes even the first).

The two steps to being (more) original are
1) Know the history of you medium/field/passion/hobby
2) Find your unique voice as in - what do you want to ADD as opposed to just wanting to belong, which is where EVERYONE starts.