Where can I find source code for STDES-2KW5CH48V

If it's not on the Product Page, that usually means that it has to be requested direct from ST - possibly under NDA.

Either:

• Raise a support case here: https://ols.st.com/s/
• Or contact your local FAE or distributor: https://www.st.com/content/st_com/en/contact-us.html

PS:

See this reply by @Peter BENSCH (ST Employee) to the same question back in 2023.

See also: Is STDES-2KW5CH48V available for purchase?