Using Windows Registry (if Config Editor isn’t available)

This method also works and is safe for localhost development.

1. Open PowerShell as Administrator.

2. Run:

   reg add "HKLM\SOFTWARE\Microsoft\IIS\Parameters" /v EnableHttp2 /t REG_DWORD /d 0 /f
   reg add "HKLM\SOFTWARE\Microsoft\IIS\Parameters" /v EnableHttp2OverTls /t REG_DWORD /d 0 /f
   
   

3. Restart IIS:

   iisreset
   
   

This completely disables HTTP/2 globally for IIS.

To re-enable later, just run the same commands with /d 1 instead of /d 0.