Messenger for Desktop stores its data in a SQLite DB. This DB is located in %LOCALAPPDATA%/Messenger on Windows. If you know the location on macOS let me know.
In the contacts table, there is a rank column. It is unclear what this rank column represents. It may be related to how Facebook Messenger ranks your friends for the list of active users.
This page lets you open your DB and plot the rank metric for all contacts with rank > 0. All the computation is done locally -- no data is uploaded anywhere. The only remote calls on this page are for Google Analytics.
To select the correct file on Windows, navigate to %LOCALAPPDATA%/Messenger in the file picker dialog and pick the .db file.