In SXA when you create a partial design for the footer, header, or any, it will not give you a rendering layout file, where you can update the HTML. It's an OOTB feature.
You can create a partial design by going into your SXA site -> Presentation -> Partial Design. And using the insert option, you will be able to create a new one.
After creating the partial design, you can add renderings to this by using Experience Editor or going into the item presentation details.
