This Starship is staying near the moon
Congress has a gun pointed at NASA's budget so Astronauts will be launching in an Orion on an SLS and returning to Earth in that Orion. SLS is not powerful enough to get to low Luna orbit so NASA needs a ride from near-rectilinear halo orbit to the Moon and back.
A fully refuelled starship in low Earth orbit cannot land on the moon and get back to the surface of the Earth. If Starship refuels in a highly elliptical orbit it can almost go to the Moon and back - but the fuel tanker has to be refuelled before it can reach that orbit. Add the stops at NRHO to dock with Orion to pick up and return the crew then a normal Starship cannot meet NASA's requirements.
The plan is to use a modified Starship with no flaps or heat shield. This Moonship cannot return to Earth but it can go to NRHO, land on the Moon and return to NRHO. A normal tanker Starship could get refuelled in a highly elliptical orbit, go to NRHO, refuel the Moonship and return to Earth.
The Moonship mission sidesteps the big certification problems that will otherwise delay a normal passenger Starship: Launching a crew with no launch abort system, re-entry with a new thermal protection system, getting velocity down to subsonic while falling like a skydiver, a belly flip to get the engines pointing down and a retro-propulsive landing. It will be a long time before NASA is happy to put a crew on a mission with all those exciting activities but in the mean time Starship tankers can RUD without killing anyone until SpaceX get it all working reliably.