According to a report from MacGeneration, it seems that the macOS version of Messenger is currently being rolled out in France. It seems that this could be a phased rollout because there are reports that the app isn’t available yet in other regions, but give it some time and it should eventually find its way to you.
Also, as noted by 9to5Mac, it seems that the version of Messenger for macOS was built using Electron, as opposed to Mac Catalyst, so that’s something to take note of. It also seems that the desktop version of Messenger is similar to its web counterpart in terms of functionality, so if you’ve used the web version of Messenger, then the desktop version shouldn’t be too different or prove to be too steep of a learning curve for you.
In the meantime, Facebook has also updated its iOS version of Messenger where they have made it faster than before while having a smaller footprint.