I'm Baptiste, part of the development team at Prismic, and I'm happy to welcome you to our community.
We're aware of this issue and tracking it. I'll come back to you as soon as this is resolved, but in the mean time, you can manually copy and paste the following Custom Types into the Custom Types Editor to get started (
Menu shall be "Single Type" and
Page shall be "Repeatable"). If you're not aware of the ability to edit Custom Types using JSON, I advise you to read the following documentation: Introduction to Custom Types building and How to version custom types. After you've created your Custom Types, you'll have to create documents that match these Custom Types (you'll at least need a Homepage and a Menu for the Next.js app to run properly).
Feel free to ask further questions if you need any help.