CUSTOMIZABLE FOUND? Come in to understand <<<<<

a while ago I saw a video on tik tok!!11211 I said something like... EEEEEY LOOK it's youtube buuuut customizableee111111! and I said OH BOY this is great but I lost it, I REMEMBER VERY BADLY about them uploading something, gore there, oh, I don't want that because of that, I just want to customize another place, you know? it looked like Space hey if you get it comment PLEASEEEEEEE