Facebook applied for a patent related to a field that is far from its interests, namely smart phones, specifically the unit type. The patent application presents a model for a unit telephone consisting of several parts that can be installed on each other.
The picture currently available is somewhat ambiguous, as it is not clearly a smartphone, but may be a smart home audio assistant.
But you can see that there are audio speakers, microphone, touch screen and GPS.
The idea of a home helper seems more logical now as most major companies are launching a device of this category, especially since the concept of modular smartphones has not received the attention of users.
Facebook has a special section of secret projects called 8 Building 8, where many of the employees who worked on the project ARA, the unit phone that Google began to develop and then stopped the project.
In any case, just applying for a patent does not mean the company intends to develop the device and actually launch it, but it may be for the protection of ideas only.