They’ve started signing a handful of customers:

https://en.wikipedia.org/wiki/List_of_Starship_launches#Future_launches

NASA just bought another one to deliver the JAXA pressurized rover:

https://www.nasa.gov/news-release/nasa-plans-to-assign-missions-for-two-future-artemis-cargo-landers/

And some companies are starting to design with Starship in mind, like K2, Vast, and Gravitics:

https://www.k2space.com/blog/introducing-k2-space-building-satellites-for-a-post-starship-future

And still not a customer in sight for this useless POS.

Their primary customer is Starlink, and a big chunk of ship development is being paid for by Starlink revenue.

The internal video of the payload bay shows part of the mechanism that will be used for them. Probably a few more launches and splashdowns and then it will be carrying Starlink sats as test payloads.

To maintain the full Starlink constellation they need to launch about a thousand satellites a year. There’s your customer for “this useless POS” right there, and they didn’t even have to look outside their own organisation.