Upto what frequency i.e. 5 , 10 or 20GHz can RFCMOS designs be done with open source sky130 PDK ? Are SPICE models available in sky130 PDK been characterized using S-parameter data ? As per foundry upto what max. frequency does these models support RF designs ?

No actual AC measurements data is available for now. Simulation with the PDK shows 100GHz fT for the shortest channel length transistors, which I think is reasonable for 130nm. EM sim shows that the inductors can have Q of 10 in the 5~10GHz range. It means you can get a good bandwidth & gain at 10GHz I think

But without High frequency AC data included in simulation models it would be risky to do any design for industry requirements. There might be significant deviation between simulation and post fab Rf measurement results. Especially at 10Ghz.

Exactly, There's a repo of raw data measured (https://github.com/google/skywater-pdk-sky130-raw-data), I hope they are going to do AC meas. soon.