According to a news article on Seibertron which sites an interview, there are not one but two sequels in development. One could be considered Transformers 6 and the other considered Bumblebee 2.

Guess it kinda makes sense. Bumblebee was very popular with the critics, the other movies were very popular at the box office. So by continuing both they are trying to please everyone (good luck with that considering what the TF Fandom can be like )

Anyway, the link is HERE