TL;DR: Wi-Fi says “No internet, secured”: connected to the router but nothing loads

The fix only. No explanation, no diagnosis. Read the full article if any of this does not match what you are seeing.

1. Check whether it is just this PC. If a phone on the same Wi-Fi also has no internet, the problem is the router or the internet provider. Restart the router and stop here.
2. Turn Wi-Fi off and on, restart the PC, then forget the network and join it again.
3. Read the address Windows was given.

ipconfig /all

• 169.254.x.x: no DHCP address. Go to step 4.
• A normal address but no Default Gateway: go to step 4.
• Address and gateway present: it is DNS or something blocking traffic. Go to step 5.

4. Renew the lease on the Wi-Fi adapter. Use the adapter name shown by ipconfig.

ipconfig /release "Wi-Fi"
ipconfig /renew "Wi-Fi"

5. Test the layers one at a time.

ping <your default gateway>
ping 1.1.1.1
nslookup www.msftconnecttest.com

Then open http://www.msftconnecttest.com/connecttest.txt in a browser. It should say Microsoft Connect Test. A hotel or airport sign-in page appearing instead means a captive portal: sign in there.

6. Disconnect any VPN. In ncpa.cpl, open the Wi-Fi adapter properties and look for filter items from VPN software you no longer use.
7. Flush the DNS cache.

ipconfig /flushdns

8. Last, the heavy reset. It needs a restart and removes static IP settings. Save them first.

netsh -c interface dump > %USERPROFILE%\netconfig.txt
netsh winsock reset
netsh int ip reset

After this reset, a PC with a fixed (static) IP address goes back to automatic. Re-enter the static settings from the saved file, or netsh -f %USERPROFILE%\netconfig.txt after the restart.

← Full article, with the diagnosis and the why