i cant open it idk why : (

this isn’t an installer, it’s an mod for fabric. If you just want optifine get it from here and select mirror next to the version you want, then run that. If you still can’t open it, get java from https://java.com then try again.

As mentioned, OptiFabric is just a normal mod file which you put straight into the mods folder, no running it required. If you're having troubles installing Fabric there's a helpful set of pages on it on the wiki.