The version requirement for cmake in the datadog-agent port is overly new and prevents the port from building on even slightly older ports trees where the datadog-agent otherwise runs just fine.
The Makefile specs cmake>=3.18:devel/cmake but the Datadog Agent docs at https://github.com/DataDog/datadog-agent specify a minimum cmake version at only 3.12.
I'd like to suggest that the Makefile reflect the Datadog agent docs and not the most recent version of cmake available from FreeBSD ports.
I'd provide a patch, but it seems a bit overkill for a single character difference in the Makefile. :)
And, most importantly, thanks for building the port! It is working quite nicely for us.