OpenSSL 1.1.1 will conflict with *SSL from ports but not the Base one, which is the default.
IIRC the syntax would be something likewww_nginx-devel_DEFAULT_VERSIONS+=ssl=openssl111
.
I think I saw sidetone using per port configurations in the past.
Are you sure that /etc/make.conf allows to use different default versions per port?
I try to compile net-snmp with base openssl instead of openssl port.