It is believed that at one time DC was planning to release a Batman Beyond animated movie, but due to it being put into development by Walter Hamada, who once was in charge of the DCEU.
According to John Rocha and Jeff Sneider, the film was written by Dan Casey, but it is unknown whether we'll see it, as it was commissioned by the old guard of the DCEU.
James Gunn and Peter Safran have cancelled a few DC projects to better shape their upcoming reboot of the universe.
The Batman Beyond movie likely wouldn't fit in with the timeline Gunn and Safran are going for, as it would be a film set in the far future, covering a completely different Gotham City from the one we're used to. But, if Matt Reeves' Batman universe is left alone, perhaps there could be space for a Batman Beyond animated universe too.