How to define those two SAR Technologies?
PolSAR and InSAR are two fundamentally different parameters.
PolSAR looks at different polarities within one observation, so whether the signal is 'vertical' / V, or 'horizontal' H, when the signal was emitted and when it is received. This is why you'll often see a SAR dataset labelled with either VV, VH, HV, or VV (theoretically, VH and HV should be the same).
InSAR looks at the phase of the phase in the signal of two or more observations. The idea here is to look at the difference in phase to identify areas of deformation, such as areas suffering from subsidence.
Overall, the two methodologies have fundamentally different use-cases, with PolSAR being more in line with other remote sensing methodologies and InSAR being quite unique in how it is done and what it can do.