How does UE estimate the SSB received power?

Hi All, a question on initial acq using SSB block.
How does UE estimate the SSB received power?
Is it through measuring the SSS?
Or the DMRS in SSB block?

It can be both, but primarily SSB-RSRP is measured on SSS.
PBCH DMRS can be additionaly used for the same.

Ok, but why only SSS?
Why not PSS?
Any idea?

Because PSS comes before PBCH (contains DMRS) in time domain.
So normally SS RSRP is used because it comes after PBCH (DMRS).