1- Open the Mac Terminal accessing to the Spotlight icon.

 

 

2- Start typing terminal in the search box.

 

 

3- Once it find the app, double click in the Terminal icon to open the terminal window.

 

 

4- Type sudo su - root to become a root user.

5- Type defaults write /Library/Preferences/com.apple.networkd tcp_connect_enable_tls13 1 command and press Enter.

6- Restart Safari.

Note: If you are using Safari version 7 or greater, TLS 1.1 and TLS 1.2 are automatically enabled.

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