This is not a RawTherapee issue but a lensfun limitation (which is used by RawTherapee).
I just had a look at which iPhones lensfun supports: 1, the iPhone XS. And only the 4.25mm f/1.8 and 6mm f/2.4 back camera.
You could upload a RAW and create a ticket to get it included (Lens calibration / Upload calibration pictures).