RV&S 12.3 does support MATLAB 2019b - for more information do visit the PTC Support site to access the Platform & Integration documents.
But, referring this document : https://www.ptc.com/-/media/45093724EC844E1F9EEF8D9E9892A116.ashx?sc_lang=en , it says for 12.3, Matlab is supported till 2019a. Can you share me the link of updated document?
Apologies for the miss below, I should have typed "does not support".
Having said that, 2019b is planned for 12.3.1 that comes out at the end of June 2020.