While on the promotional tour for his new film The Accountant (which opens October 14), Affleck mentioned that the DCEU’s first Batman standalone would simply be titled The Batman.
Affleck is co-writing the script for that film with DC’s own Geoff Johns, and is in line to direct.
The Batman is certainly a plausible option, as it’s straightforward and enough of a departure from previous Batman films.
Christopher Nolan’s trilogy relied more on the “Dark Knight” nickname than Batman, so there shouldn’t be any confusion if that’s the route Affleck takes.