User690216013 posted
If I only publish the SSL site to Internet and prevent anonymous acces and activate basic authentification, is that enough? (Server2019)
HTTPS + Basic authentication can only solve part of the security challenge, but they are far from enough.
You still need much more measures (especially related to the site itself, like web framework/code) in order to achieve better security.
Hire a security consultant so that he/she can help you out.