Why are my images limited to 12MP?

When in Photo Mode you first select what Process to shoot with, you have four options: Natural, Raw, Standard, and ProRaw.

Natural and Raw both utilize Bayer Raw image data which is locked to only 12MP and can not utilize virtual focal lengths.

So if you find your self with those options missing or un-selectable, first: Check if you are in Photo Mode and what Process you are using.