NeoLoad uses OpenJDK 1.8.0_252 and the support of TLSv1.3 is not available yet. It seems that this support will be added starting 1.8.0_272.

You can check the enhancement on OpenJDK bug site  here that mentions that information.

So support of TLSv1.3 will happen only starting from that 1.8.0_272 version.  I can't tell if and when NeoLoad will start to embed that version.