The ProtocolVersion property sets or returns the current
HTTP version number. It is used to determine how requests are
submitted to the server, as well as what header fields are required.
The default value for this property is "1.1", and should be
changed before any connection attempt is made by the client. It is
recommended you use this default value to ensure the broadest
compatibility with most servers and Windows platforms.
Setting this property to a value of "2.0" specifies
the client should use the HTTP/2 protocol standard defined in RFC 7540.
This protocol version is a significant change from previous versions and
can provide improved performance with header compression and optimizing
how requests are serviced. However, this version should only be used if
the server supports HTTP/2 and the client is running on Windows 10 (Build 1903)
or Windows Server 2019 or later versions. Earlier versions of the
Schannel SSP do not support the features required for a secure
HTTP/2 connection.