When I connect to a Wi-Fi access point on a 2.4 router or on a mobile hotspot on my cell phone (which is 2.4 g as well) it connects perfectly but doesn't browse through the internet.
Once I change to a 5g WIFI router it browse fine.
I attached the ssu when connected to a 5g WIFI and when connected to a 2.4 g WIFI
Since the 2.4GHz Internet connection is not working from both devices (your router and your hotspot on your mobile), I assume that the problems is in Windows settings, since both radios on AC8265 are working also. Once you are connected to router 2.4GHz, open Windows settings, Update & Security > Troubleshoot and then on R.H side click on Internet Connection - follow instructions. Repeat this also with Incoming Connection troubleshooter. Finally, Network Adapter will troubleshoot the AC8265 adapter also.