How to use the 3G modem of a Panasonic CF-20 toughbook for location and time services?

I got myself a Panasonic CF-20 Toughbook for some outdoor fieldwork. Some of that fieldwork require accurate time and I can not rely on network time sync. The CF-20 has a Sierra Wireless EM7305 Modem I can use to read GPS data.

I have installed Fedora 35 Workstation (Gnome) on that device. Now I try to figure out, how to get GPS location and GPS time synchronization running.

Following Enabling GPS location in ModemManager | SIGQUIT I was able to read the GPS data using modem manager. This tells me, that the modem works but checking Gnome Maps, I do not get an accurate position. The logs hint a permission issue, I have no idea how to solve.

Apr 18 07:33:28 fedora systemd[1]: Starting Location Lookup Service...
Apr 18 07:33:28 fedora systemd[1]: Started Location Lookup Service.
Apr 18 07:33:58 fedora geoclue[1837]: Failed to set GPS refresh rate: GDBus.Error:org.freedesktop.ModemManager1.Error.Core.Unauthorized: PolicyKit authorization failed: not authorized for 'org.freedesktop.ModemManager1.Device.Control'

But then, my actual goal is to get time synchronization working. For this, I have found Panasonic CF-20 Toughbook - EM7355 GPS Setup under Ubuntu — The Tech Prepper as a starting point. But here I have an issue and a question.

The issue is, I can not enable the unmanaged mode. The error indicates that the modem does not support that mode. According to the guide I used, that should be the case, though.

[user@fedora ~]$ mmcli -m 0 --location-enable-gps-unmanaged
error: couldn't setup location gathering: 'GDBus.Error:org.freedesktop.ModemManager1.Error.Core.Unsupported: Cannot enable unsupported location sources: 'gps-unmanaged''

But then, I wonder, if I have to set up and configure gpsd or if Fedora uses a different tool for GPS time synchronization (like geocode is used for location services).

So, what is the canonical way of Fedora 35 to use a 3G modem with GPS support for location services, and more importantly, for time synchronization?