So I recently quitted Google Drive

Congrats, great life choice

downloaded all my data and hoping to keep it on Hard drives myself, They are external plug in types

You have multiple external drives. Are they USB? How many?

So when I plug it in

Are they not usually plugged in? Is there a requirement to keep them air gapped between syncs?

it copies/syncs the things on my computer, anyone knows somethign like that?

Like others have said, a shell script that calls rsync is maybe the way to go and with some more information on number of drives, drive interface type, and air gap requirements it may change