Make more misotheist characters
In DnD settings such as Faerûn and more recently in the Cosmere, where the existence of gods or god-like beings has been proven beyond the shadow of a doubt, having an atheist character makes little to no sense. Why would you deny the existence of gods when there's people who can literally channel divine power to heal, harm or even resurrect others, you can talk to it and you refuse it's existence? Bit crazy.
Now there's a somewhat roundabout way in which you can justify the existance of atheism, a lot of the time in these worlds gods can be fought, replaced and killed; there are god corpses in the Astral Plane and Adonalsium and its Shards have been frequently shattered, entrapped and modified. An atheist character could argue that, since none of them have proven themselves to be trully omnipotent, none of them are trully godly and are just extremely powerful, but ultimately mortal, beings.
I would like to propose, however, an alterntive. A character that not only recognizes the divinity of their gods, but who also detests them for it. We're taking off from the idea that gods exist and, while not omnipotent, they are divine and beyond human reach, that they have stablished followings and that someone, for some reason, may hate them for any or all of these characteristics. What are their motivations? They could be anything really, a real life example is the backlash against the church during the French revolution and the rise of the Cult of Reason; while not misotheist, a fantasy Robespierre could see the very existence of the gods as inherently monarchic and oppressive decide to take no gods, no kings to it's logical extreme. Whether they are truly divine or just very powerful in your particular world would dictate the degree to which this misotheist project succeeds.