how to Declare a custom type on Next.js NextPageContext?

Question

N Next JS version: 11, I add a custom NextPageContext type for typescript! following this three step:

BUT in Next JS version: 12, I want to add same custom NextPageContext type for typescript; Bt is throw a ERROR 'Property 'isMobile' does not exist on type 'NextPageContext'.ts(2339)'; so how can i add Custom type in NextPageContext??