Forking in Github


I have a noob question that on the face of it looks logical, but assuming stuff tends to always end the same way.
I’m working with git on a very basic level daily, but this is some advanced stuff I have no knowledge about.

I forked a project in GitHub, that is no longer being developed, or supported.
I tidied up the code, made some changes to my own forked project, but it came with lots of garbage sub-branches I have no need for. I want to make my repo clean and contain only the stuff I need.

Can I delete the non-main branches in my repository without it having any effect on the project I forked it from?

I would think that what happens in my repo, stays in my repo, but I don’t want a situation where at some point someone says: “… aaaactualllyyy!”