SLC Calibration and C2 Elements

I would like to know how one can arrive at Gamma0 while processing SLC data since I notice that at the calibration step the moment I select ‘save as complex output’ the ‘Output sigma0 band’ option is selected alongwith it.

Furthermore, I would like to know if the elements of the complex C2 matric are actually the Sigma0 VV and VH in case of the dual-pol Sentinel-1 data.

You either select complex output OR Sigma0/Gamma0. The fact that Sigma0 is still selected in grey shouldn’t matter.
If you want Gamma0, de-select complex output. If you want terrain flattened Gamma0, select Beta and proceed with Radiometric Terrain Flattening

Which means that even if I don’t select ‘save as complex output’ and go ahead with the beta0 processing, the final output will be complex when I do RDTC.

no. Complex output will give you a calibrated intensity band. You cannot have both complex and sigma/beta/gamma at once.