Turning on GPS (GNSS) is not in and of itself a problem - because GPS (GNSS) is purely passive from the point of view of the phone. The issue is what happens with the coordinates that the phone derives.
Do they get transmitted automatically by the phone to the MNO or to someone else?
Is this only when you call 911 or is this continuously or something else?
Some (most? all?) cellular modules have GNSS built-in, and one could speculate as to whether this is bad for privacy. In a blackbox phone (Apple / Google) it doesn’t matter so much since you are kidding yourself that you control whether the GNSS is enabled or whether the coordinates are transmitted, when and to whom.
In the Librem 5 I believe this is mitigated by ensuring that the cellular module is not connected to the GNSS antenna. I am not an electrical engineer so I don’t know whether that is adequate (since obviously the cellular module is connected to an antenna, but the antenna may be optimised for cellular use, not GNSS use).
The cellular module may provide AT commands to control its use of GNSS but you can never truly know whether the AT command was actually effective or only appeared to be effective - unless you can get an open source cellular module.