I found this error message when compiling some software from source:
It looks like you're compiling on Linux and also targeting Linux. Currently this
requires the `pkg-config` utility to find OpenSSL but unfortunately `pkg-config`
could not be found. If you have OpenSSL installed you can likely fix this by
installing `pkg-config`.
Luckily, it’s an easy fix!
$ apt install pkg-config
On Debian 12+ and Ubuntu 23.04+ that pkg-config package is now a transitional one that pulls in pkgconf, but you don’t need to change anything: it still provides the pkg-config command and the install works the same way.
This’ll install the required binary:
$ which pkg-config
/usr/bin/pkg-config
And you’re all set!