https://screenrant.com/transformers-last-knight-sequel/
Transformers 6 = sequel to The Last Knight.

Now before we all lose the plot, please bear in mind that MICHAEL BAY WILL NOT BE DIRECTING, and as Travis Knight as shown us, it is possible to make a good Bayverse movie with a different director. Because Bumblebee on its own isn't a definitive reboot or prequel, it's rather ambiguous which I think was a deliberate decision on the studio's part to leave their options open. We know that the original cut was a more definitive prequel but then edits were made to make it more ambiguous. So Bumblebee could still very easily be retconned as a prequel.

And The Last Knight did finish with some interesting story ideas, such as...
* Earth = Unicron
* Unicron being the ancient enemy of Cybertron
* Cybertron has come to Unicron
* Unicron is awakening
* Quintessa survived and is on Earth posing as a human
There are some potentially decent story elements here, we just need to good director to pick the ball up and run with it, and importantly, give us a good story that isn't a "rinse, lather, repeat" of the Michael Bay films. Cos that was the thing that was bugging people with Bayformers, it had become too predictably formulaic - as demonstrated by The Nostalgia Critic's Not Review of The Last Knight which was fairly accurate in predicting what would happen in that film before it was even released.

Bumblebee isn't the most original idea in the world - it's basically recycling the plot from films like E.T. and The Iron Giant (etc.), but it's a good story and as far as the Transformers cinematic universe is concerned, it was a different story. Movies don't need to be perfect, they just need to be good and entertaining. The MCU has proven this to us many times over.