Cant connect to Synology RT2600ac

Here is what you requested. The signal strength screen is very good. RSRQ -10, RSRP -96, SINR -10. I do not believe that a weak 5G signal is the issue; what happens on the cellular side should impact connectivity on the Wifi side of the GW; it may impact performance, but that's not the issue here. In any event an Ookla speedtest on my cellphone which readily connects to the 5Ghz Wifi band reports 248 Mbs. The phone is less than 3 feet away from the RT2600ac Router