SSLScan queries SSL services, such as HTTPS, in order to determine the
ciphers that are supported.  SSLScan is designed to be easy, lean and
fast.  The output includes prefered ciphers of the SSL service, the
certificate, and is in Text and XML formats.

Upstream recommends building statically against OpenSSL 1.1.1 for the
widest compatibility for scanning. You can build against the system
openssl with:

STATIC=no ./sslscan.SlackBuild