Turn Location Services and GPS on or off on your my iMac?

There is no GPS on an iMac.

The iMac does not, and never has had, GPS built in. The iMac estimates its location by using WiFi signals it sees in the area to triangulate its position. It’s just a guess and not GPS.

As for Location Services go to System Preferences->Security & Privacy->Privacy->Location Services. There you may remove or add apps that are allowed to use Location Services.