I'm going to be super honest with you: I don't actually think it matters if someone copies your story.
If someone read part of my story and tried to tell their own version of it, I'd be a little miffed if it were super close, but it would eventually turn into a completely different story. Because like.... the actual beats of my plot aren't what makes my story good. The interactions that the characters have and the way they change and grow through that story, and the experiences that I have and the things that I love and care about, all come out through that story. The story is good because I personally love it, and I made it out of things that I love.
Someone else trying to tell that same story couldn't capture that. It'd be like stealing an invention from a mad scientist and then realising you have no idea how to actually use it.
I can't guarantee that no one will steal your ideas... but I also can't guarantee that nobody will have the same ideas as you. What if you keep your story locked away, and never share it in order to keep it safe, and somebody else just... has the same idea one day, and makes a comic out of it? That happens! That happens a lot more often than stealing stories does!!
So I think you have to get rid of the idea that your story is only good if it's unique. If someone else has the same idea as you, or is inspired by your idea and makes something similar, that's okay!! because your story will probably turn out very different. You like different things and care about different parts of it and different parts of the idea resonate with you. Someone who just runs off with your ideas won't know how to make them good, or what to do with them.
(Also, if you create and publish something on the internet, in the US that means your story is automatically copyrighted. There's a way to register a thing after you've created it, to make it easier to prove in court, and it doesn't hurt if you wanna look into that -- but like...... none of us actually want to go to court over this. If someone else makes a story about a thing that you made a story about, do you really want to go to court to try to make them stop?? Or do you just want to keep telling your story?)
