After Bumblebee became a success, there was a rumor going around that a spinoff focused on Optimus Prime would be in the works. Unfortunately for Optimus fans, the movie looks to have been shelved.
According to The River (via Fandom), the movie looks to have been put in the backburner, with Paramount focusing on putting Prime in the spotlight along with Bumblebee in the Bumblebee sequel. The movie is being described as a buddy-cop film, so I guess it's just as good as getting a solo movie.
Either way, Prime works best when he's the leader of the Autobots. It would be weird to have him star in a solo movie without a team behind him to lead. I guess it kind of worked with Bumblebee since Bee has always been the hero/rookie type who kind of has his own story to tell.
If anything, it has also been confirmed that the studio is working on making a sequel to Michael Bay's The Last Knight, so we could still be seeing more of Prime in the future. I just think it's weird that they would come back to that franchise, seeing that there's been positive reception with Bumblebee and the Bay films have been getting a worse rep with every film that comes out.
If you ask me, they should just work on a G.I. Joe reboot and cross them over with the Transformers down the line. I mean, both properties are under the Hasbro banner. Imagine the merchandising they could come up with.
No release date has been set for the Bumblebee sequel.