After a long search, I found a working LTE modem update file from version EG18EAPAR01A08M4G to version EG18EAPAR01A11M4G.
Go to Orbi LBR20 | WiFi System | NETGEAR Support
Select the European/Australian or American version respectively.
We choose whether we want to update or downgrade the LTE modem.
After downloading the .zip file, go to the configuration page of our router and select the LTE modem update option.
We select the zipped .zip file.
The update in my case on the Zyxel LTE5398-M904 router took 15-20 minutes.
I haven’t tested the downgrade file.
The update file I received from tabor.tang-Q does not work. It differs in file weight, it is 104 MB, while the upgrade/downgrade file is 40 MB.
It seems to me that if your router has a Quectel EG18EAP modem, then you can update it. In case, after uploading the file and clicking “Update”, an error message will pop up.
In case of removing the link to the modem firmware, I will write that we are looking for “Netgear support” in Google, enter the model “LBR20 - Orbi LTE Tri-band WiFi Router / LBR20”, click the “Downloads” button, then select "LTE Upgrade / Downgrade Package (Retail - Europe / Australia).
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