groove_untie145 Turning "reroute location requests to the OS" off means that apps asking Play Services for location information will receive the information from Play Services instead of from the OS. At present the OS supports only pure GPS, which is great from a privacy perspective but doesn't determine location as quickly or as well.
As indicated in the other thread, running GPSTest or the equivalent can shed light on what's happening. If GPSTest can't establish a GPS lock, the present GrapheneOS location provider also can't.