Usually, the option to make traditional projects is at the bottom of https://www.inaturalist.org/projects/new. I used it earlier today, but it has since gone missing.
Investigating, looks like a bug.
In the meantime, you can just go straight the URL for making a new trad project: https://www.inaturalist.org/projects/new_traditional
Sorry about that folks, mea culpa. Should be back.