The Transport Layer Security version 1.3 standard is the latest and greatest version of SSL available. It offers increased security when compared to older TLS standards. By default, cPanel supports multiple TLS versions at the same time for backward compatibility. What are the drawbacks of disabling TLS versions prior to version 1.3?
An up-to-date listing of browser compatibility can be found here from Can I Use.
Mail client support for TLS v1.3 is limited.
Thunderbird also supports TLS v1.3 by default.