Grx 10 speed problem
@ArgentiApparatus is correct - 9 clicks is 10 speeds.  Your lever starts at one end, in a gear position, and the first click puts it into the second position.  Thus there is one fewer click than gear positions.
You definitely have a 10 speed shifter, confirmed by  https://bike.shimano.com/en-EU/product/component/grx-10-speed/ST-RX400-R.html
There remains the possibility that the shifter is somehow faulty, or that your indexing is not correct.