Inquiry Regarding Supported Databases for the Read-Only API

Regarding the documentation at https://help.sonatype.com/en/read-only-api.html:

The manual states, “This feature is only appropriate for installs that use the legacy OrientDB embedded database.”
I would like to confirm the detailed meaning of this statement.

My understanding was that by performing a “freeze,” it is possible to prevent input from the GUI and block updates through the API. However, does this statement mean that the read-only API cannot be used if PostgreSQL is used as the database?

In our operational verification, it appears that the freeze function of the read-only API prevents updates from the GUI as expected. We would like to clarify what the actual limitations are.

Thank you in advance.