To disable HTTP/2 on Windows 10 HTTP.SYS, set the following registry value on the Windows 10 desktop in HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters
EnableHttp2Tls REG_DWORD 0
EnableHttp2Cleartext REG_DWORD 0
The second of these is only necessary if the failure is with HTTP. The first is for HTTPS.