Unable to connect to internet over Wi-Fi

Good afternoon,

Following the recent Windows 10 Update it took much longer for my PC to establish an internet connection. This then became intermittent and now it won't do it at all. It will say it's connected to the network, and that it has internet access (although it takes longer to get this information than it used to) but I can't connect to the internet.

When I ran the network diagnostic tool it initially came up with the following error:

Primary DNS server not responding (I can't remember the exact wording and can't reproduce it now)

Having tried some fixes it now comes up with:

Wi-Fi doesn't have a valid IP configuration.

All other devices in the house are connected fine, and I am currently submitting this tethered off my phone which is connected to the Wi-Fi.

I have tried a number of fixes suggested online:

Restarting my PC

Restarting my router

Updating my network adaptor drivers (they did need an update but it didn't solve the issue)

Uninstalling my network adaptor and then having windows reinstall and update it.

Releasing and renewing my IP address

Flushing my DNS info (not entirely sure what I was doing with the last 2, just following isntructions)
Finally, re-installing windows, but opting to keep my apps and files. I do now get a slightly different error from the diagnostic tool:

Default gateway not available

None of this has got me anywhere, I can still connect to the network but not the internet. The network sign on my task bar intermittently shows connected no internet, connected with internet, not connected, but regardless I can never access the internet.

I am running Windows 10. hardware details are:

Network Adaptor - Intel(R) Dual Band Wireless AC 3168

Processor - Intel(R) Core(TM) i3-8100 @3.6 GHz

RAM - 8GB

Anyone got any ideas? I'd rather avoid wiping everything and starting again if I can.