Where does “विसर्ग” come from?

विसर्ग (Sanskrit) comes from Sanskrit सृज्, from Proto-Indo-European selǵ- — to let go, send.

Ancestry of “विसर्ग”, step by step

Step	Language	Word	Meaning
1	Sanskrit	सृज्	to cast or let go; to throw, cast, eject
2	Proto-Indo-European	selǵ-	to let go, send

विसर्ग — Etymology, Origin & Word History | Etymology Explorer