When I opened the .def file (generated after floor plan stage) in magic, I didn't get any metal layers(blue) and active layers (pink), just the standard cells and tap cells. Am I missing any switch ? Thanks in advance.

Maybe try using the

-rcfile $PDK_ROOT/$PDK/libs.tech/magic/$PDK.tech

option.

magic -T home/pa1mantri/.volare/sky130A/libs.tech/magic/sky130A.tech lef read ../../tmp/merged.nom.lef def read picorv32.def I did include the tech file