The online manual has some details about how MongoDB Enterprise Server can be configured to use FIPS 140-2 certified libraries for OpenSSL (https://docs.mongodb.com/manual/tutorial/configure-fips/)

This documentation is:

1. Very Linux-centric. MongoDB Enterprise Server for Windows also supports FIPS 140-2 mode, so the docs should at least mention that.
2. Network (TLS/SSL) focused. The Encryption At Rest engine will also make use of FIPS 140-2 mode once it is enabled, so that docs should mention that too.