How DC Can Craft The PERFECT Shared Universe On HBO Max
3. Then Do Green Lantern(s)
Much like Justice League Dark, Green Lantern has the benefit of not having to involve the Justice League (except for its Lantern members, obviously).
This show should have most, if not all, of the human Lanterns already established and should take place almost exclusively in space - as Earth-based Green Lantern stories are simply not as interesting, plus it would be another excuse to avoid the League.
If it were down to me, then the first season of this show would be all about Sinestro's downfall and the creation of the Sinestro Corps. Sort of like what the Star Wars prequel trilogy did for Anakin Skywalker and the Empire, with Hal Jordan filling the role of Obi Wan (but as the mentee rather than mentor) in this analogy.
Alternatively, DC could not do that - they've just got to keep whatever they decide to do in space.