Frequently Asked Question about TLS and Cipher Suite configuration

I don't understand the statement that "The protocol is not available in down level OS versions" as it does exist and can be enabled.  It is, however labeled as 'experimental' in some places.  I have read elsewhere that "Enabling TLS 1.3 on earlier versions of Windows is not a safe system configuration", but zero explanation was given for that.

I read that Microsoft was working on adding TLS 1.3 to Windows 10.  What happened?  Labeled as 'experimental' says to me that it is there, but is in a beta or release candidate state, at minimum.  Most things I have read about .NET Framework 4.8 says that it adds support for TLS 1.3, which says to me that TLS 1.3 is supported everywhere that .NET Framework 4.8 is (although some OSes that it is supported on are no longer supported by MS).  Documentation on this kind of thing needs to be clearer and easier to find.