Monolithic just means it can carry out all it's required functionality alone, i.e. it's [major] dependencies are internalized.

It doesn't say anything about not being able to be broken into modularized sections, services, or domain boundaries.

Neither does it reject any setups where satellite systems, micro or otherwise make use of the monolith programmatically or otherwise, hell it's kond of part of the definition of a monolith that it has multiple access points (i.e. cli, sdk, rest, rpc, events.)