Typically the software has a default location for configuration files decided on by the developer which can be overridden at build time.
You, or typically a package maintainer and the packaging guidelines in use for that distribution, can decide on an alternate location.
The official freeradius wiki refers to both: /etc/raddb
and /etc/freeradius
A location such as /etc/raddb
might be chosen for backwards compatibility with a
different Radius server.
Where /etc/freeradius
is more obvious location and consistent location for a product called FreeRadius to store configuration files...