The IBM enabled TLS 1.2 and TLS 1.3 support with the release of DS8K 9.4 release: Does Vantage support the TLS 1.3 version?
IBM officially started supporting the TLS 1.3 protocol with the Version DS8K 9.4 release, so Vantage should support TLS 1.3. The Vantage PTF LU15025 introduced configuration of secure connections via AT-TLS, so the support of any version of TLS is purely in the configuration of AT-TLS and is transparent to the Vantage application.
The DS8K boxes prior to release 9.4 do not support TLS V1.3 . This is the main limitation, not by vantage, but by the boxes themselves.