I’ve tried tethering to GL-SFT1200 from my Motorola Edge 30 pro. When the phone was connected to the router, it started charging but there is no option for USB tethering. In “hotspot and tethering” option, “usb tethering” was grey out.
I’ve tried another phone (Samsung A73) with GL-SFT1200 which again had the same issue where USB tethering option is grey out.
I’ve tried my phone USB tethering on my desktop which worked.
First when you connect your phone to the Glinet device you have to select an option in the pop-up window of your phone “Use usb to transfer files”. Then, in the personal access point menu, the usb tethering option will be available.
In your case, I think, this USB option is only for charging, you have to chage it.
Does your USB cable support BOTH power and data? Low cost USB cables that come as “freebies” with some devices are low quality and only support power only.