https://docs.microsoft.com/en-us/dotnet/api/system.security.authentication.sslprotocols?redirectedfrom=MSDN&view=netframework-4.0

SslProtocols Enum

Definition

Defines the possible versions of SslProtocols.

This enumeration has a FlagsAttribute attribute that allows a bitwise combination of its member values.

[System.Flags]
public enum SslProtocols

Default	240	Use `None` instead of `Default`. `Default` permits only the Secure Sockets Layer (SSL) 3.0 or Transport Layer Security (TLS) 1.0 protocols to be negotiated, and those options are now considered obsolete. Consequently, `Default` is not allowed in many organizations. Despite the name of this field, SslStream does not use it as a default except under special circumstances.
None	0	Allows the operating system to choose the best protocol to use, and to block protocols that are not secure. Unless your app has a specific reason not to, you should use this field.
Ssl2	12	Specifies the SSL 2.0 protocol. SSL 2.0 has been superseded by the TLS protocol and is provided for backward compatibility only.
Ssl3	48	Specifies the SSL 3.0 protocol. SSL 3.0 has been superseded by the TLS protocol and is provided for backward compatibility only.
Tls	192	Specifies the TLS 1.0 security protocol. The TLS protocol is defined in IETF RFC 2246.

.NET Core

2.1, 2.0, 1.1, 1.0

.NET Framework

4.7.2, 4.7.1, 4.7, 4.6.2, 4.6.1, 4.6, 4.5.2, 4.5.1, 4.5, 4.0, 3.5, 3.0, 2.0

.NET Standard

2.0, 1.6, 1.4, 1.3

Xamarin.Android

7.1

Xamarin.iOS

10.8

Xamarin.Mac

3.0