Note that all OpenSSL versions that support TLS 1.1 also support TLS 1.2, so setting the minimum version to TLS 1.2 instead of TLS 1.1 would have no practical drawback for users of OpenSSL, as far as I can tell. There are PostgreSQL clients that don’t use OpenSSL, such as the JDBC driver, but it seems unlikely that the version of the Java stack you use would not support at least TLS 1.2 at this point. It is probably too early to require TLS 1.3. The protocol itself and the required OpenSSL release are only about a year old, and so you probably won’t find them in most operating installations that are currently in use.