I have my B1 visa interview in Dec 2020.?
You have to hand them a valid passport with one whole free page where they will stick the Visa. If you have a fee page and you are not sure if you can get a new passport before your interview you can go ahead with your existing passport. You can get a new passport later on, the visa on this passport will be valid and can be used. If you don't have a single free page, you will have to apply for a new passport. If your new passport doesn't arrive before your interview you can re-schedule your interview - no probs.