Thanks a lot @mocmocamoc for pushing the PR into being merged!
I don't have a 5G SIM card (yet), so I'm not able to test on my device, but as far as I can see the 5G network can be detected by the modem:
root@OpenWrt:/# mmcli -m 0
-----------------------------------
General | path: /org/freedesktop/ModemManager1/Modem/0
| device id: bbbc308cf369730622e8944f5b90a094ce8db130
-----------------------------------
Hardware | manufacturer: Quectel
| model: RM520N-GL
| firmware revision: RM520NGLAAR01A07M4G
| carrier config: ROW_Commercial
| carrier config revision: 0A010809
| h/w revision: 20000
| supported: gsm-umts, lte, 5gnr
| current: gsm-umts, lte, 5gnr
| equipment id: <redacted>
-----------------------------------
System | device: /sys/devices/platform/soc/11200000.usb/usb1/1-1/1-1.2
| physdev: /sys/devices/platform/soc/11200000.usb/usb1/1-1/1-1.2
| drivers: qmi_wwan, option1
| plugin: quectel
| primary port: cdc-wdm0
| ports: cdc-wdm0 (qmi), ttyUSB2 (at), ttyUSB3 (at), wwan0 (net)
-----------------------------------
Status | lock: sim-pin2
| unlock retries: sim-pin (3), sim-puk (10), sim-pin2 (3), sim-puk2 (10)
| state: registered
| power state: on
| access tech: lte
| signal quality: 75% (recent)
-----------------------------------
Modes | supported: allowed: 3g; preferred: none
| allowed: 4g; preferred: none
| allowed: 3g, 4g; preferred: 4g
| allowed: 3g, 4g; preferred: 3g
| allowed: 5g; preferred: none
| allowed: 4g, 5g; preferred: 5g
| allowed: 4g, 5g; preferred: 4g
| allowed: 3g, 5g; preferred: 5g
| allowed: 3g, 5g; preferred: 3g
| allowed: 3g, 4g, 5g; preferred: 5g
| allowed: 3g, 4g, 5g; preferred: 4g
| allowed: 3g, 4g, 5g; preferred: 3g
| current: allowed: 3g, 4g, 5g; preferred: 5g
-----------------------------------
Bands | supported: utran-1, utran-4, utran-6, utran-5, utran-8, utran-2,
| eutran-1, eutran-2, eutran-3, eutran-4, eutran-5, eutran-7, eutran-8,
| eutran-12, eutran-13, eutran-14, eutran-17, eutran-18, eutran-19,
| eutran-20, eutran-25, eutran-26, eutran-28, eutran-29, eutran-30,
| eutran-32, eutran-34, eutran-38, eutran-39, eutran-40, eutran-41,
| eutran-42, eutran-43, eutran-46, eutran-48, eutran-66, eutran-71,
| utran-19, ngran-1, ngran-2, ngran-3, ngran-5, ngran-7, ngran-8,
| ngran-12, ngran-13, ngran-14, ngran-18, ngran-20, ngran-25, ngran-26,
| ngran-28, ngran-29, ngran-30, ngran-38, ngran-40, ngran-41, ngran-48,
| ngran-66, ngran-70, ngran-71, ngran-75, ngran-76, ngran-77, ngran-78,
| ngran-79
| current: utran-1, utran-4, utran-5, utran-8, utran-2, eutran-1,
| eutran-2, eutran-3, eutran-4, eutran-5, eutran-7, eutran-8,
| eutran-12, eutran-13, eutran-14, eutran-17, eutran-18, eutran-19,
| eutran-20, eutran-25, eutran-26, eutran-28, eutran-29, eutran-30,
| eutran-32, eutran-34, eutran-38, eutran-39, eutran-40, eutran-41,
| eutran-42, eutran-43, eutran-46, eutran-48, eutran-66, eutran-71,
| utran-19, ngran-1, ngran-2, ngran-3, ngran-5, ngran-7, ngran-8,
| ngran-12, ngran-13, ngran-14, ngran-18, ngran-20, ngran-25, ngran-26,
| ngran-28, ngran-29, ngran-30, ngran-38, ngran-40, ngran-41, ngran-48,
| ngran-66, ngran-70, ngran-71, ngran-75, ngran-76, ngran-77, ngran-78,
| ngran-79
-----------------------------------
IP | supported: ipv4, ipv6, ipv4v6
-----------------------------------
3GPP | imei: <redacted>
| enabled locks: fixed-dialing
| operator id: 20820
| operator name: Bouygues Telecom
| registration: home
| packet service state: attached
-----------------------------------
3GPP EPS | initial bearer path: /org/freedesktop/ModemManager1/Bearer/0
| initial bearer apn: <redacted>
| initial bearer ip type: ipv4
-----------------------------------
SIM | primary sim path: /org/freedesktop/ModemManager1/SIM/0
| sim slot paths: slot 1: /org/freedesktop/ModemManager1/SIM/0 (active)
| slot 2: none
Have you switched the modem to use the USB interface, as indicated in the commit message adding support for the X3000 device?