It has less to do with Framework and more to do with OS according to the official word from MS: https://learn.microsoft.com/en-us/dotnet/framework/network-programming/tls

Windows 7 doesn't support TLS 1.3, and neither do early builds of Windows 10.

This question has been asked before without good answer because there isn't one yet:

Is there a way for Windows 7 to support TLS 1.3 (.NET 4.8)