First of all...tethering of any kind can be blocked by your service provider!
That being said, if your provider is not blocking tethering then you need to try it in safe mode to make sure that an installed app is not causing the issue.
If it works in safe mode then you will have to determine what app is causing the issue and probably delete it.
If it still does not work in safe mode then a software repair using the Sony Companion on your PC may be the fix. It is basically the same as a factory reset except that it does more than just reset your phone...it installs all new software. Either method though will mean resetting up the phone from scratch...sorry!
Now then, before doing a software repair, does it not work when you use a USB cable from the phone to the other hardware, such as a laptop, or tablet? There is really nothing to setup when using a USB cable. Maybe a different cable could be tried?
Does it not work when using the WIFI hotspot feature? There are settings that need to be configured for this option to work correctly.
Settings > Network & Internet > Hotspot & tethering > Portable hotspot settings > Configure hotspot > I recommend that you keep the Network name (SSID) that is assigned by default. Make sure to use WPA2 PSK for the security setting and use whatever password you want. Going back one screen...is "Discoverable" toggle turned on??? It needs to be turned on! Under Power save - make sure that Never is selected.
Also, I am going to assume that you know how to connect your PC or tablet to the phone to use it for internet access? That is a subject for a Windows forum. I could explain it, but not if it's not needed here.
Hopefully one of these suggestions will help.
I use both methods at different times on T-Mobile and have no issues at all. In fact, this is my only method for internet access at the moment and it worked great under Nougat and now also under Oreo.
Please remember to KUDO if I was able to help!
