I encountered the same issue and requested assistance from Fiverr support. They informed me that being a "vetted-seller" is required in order to create a Gig in that specific category. Here's the link to the "vetted-seller" application form: https://fiverr.formtitan.com/ftproject/vetted-only
In the form, you'll notice that you must specify your previous professional work samples. But I don't know what to do if Fiverr is the only workplace where you deliver professional projects. In such situation, you cannot submit previous projects and become a vetted seller. That's weird.