secrec The proxy idea is interesting, but presumably it must still share a scan of SSID's, signal strengths, and location through to the destination server.
I think the client presents a list of SSIDs and Apple provides their locations. It is not clear why the client would provide relative signal strength information. Apple can infer a location to some extent, but presumably less well than the client.
secrec That potentially tells apple even more information than they would have with a direct connection, such as "there is a grapheneos user at this location".
There are other options... Google's service... GNSS... waiting for the GrapheneOS client to support cell-site info...