I’ve been using Scrivener for years. I actually liked the screen in version 2 that allowed you to clearly and easily set out what you wanted the headers and footers to look like in compile. Now I seem to be saddled with a bunch of default options under COMPILE->SECTION LAYOUTS which mainly include a page number centered at the bottom of the page and an enormous document title at the top.
How do I edit these options? I want to use my own fonts to create small headers and footer text, including book name, PAGE X of Y, etc.
As a years-long user of Scrivener 2 myself, I found the new compile to be the biggest hurdle to Scrivener 3—but once I took the time to learn about it, it became one of my favourite parts of the update.
If you haven’t, I urge you to look at the “What’s New” section of the in-app tutorial; I also suggest you work through the “Scrivener 3 Update Guide for Scrivener 2 Users” (https://literatureandlatte.com/scrivener-3-update-guide) if you haven’t already.
More specifically for your current predicament,
In the list on the LEFT of the compile dialog, right-click on the compile format you’d like to modify.
Select Edit Format… (or Duplicate and Edit Format… if that’s greyed out)
Click on Page Settings in the left-hand column of the new dialog that opens. Now you can edit header/footer options and header and footer text.
Silverdragon already has you sorted, but I would just add that once you go to Duplicate & Edit a format, or create a new one, you will find yourself in familiar territory - the options in the Format editor are very similar to those of Scrivener 2. The main concepts you need to get your head around are Section Types and Section Layouts. Once you understand those, you will see that you can create all the formats (and more) that you could in Scrivener 2, but that you can use them with a much wider range of projects, because the Section Types/Layouts arrangement avoids the one-format-fits-only-one-project-structure limitations of Scrivener 2’s Compile.