We won’t know more until The Flash actually starts filming and enters into post-production which, considering its many delays and directorial changes not to mention current events, could still be far off.
That would, in theory, help set up the appearance of Michael Keaton’s Batman since in the story the Flash messes with time travel in an attempt to save his mother.
But rest assured that CinemaBlend will keep you updated on the latest as more details become public.
Of course, all of this is speculation at this point.