Maxperson
Morkus from Orkus
I dont get too deep into the lore of Eberron. (Heh, and its creator advises not to.)
But as far as I know, ‘gods’ dont objectively exist.
For example, the Silver Flame (generally characterized as monotheistic) associates with various magical phenomena, such as a supernaturally empowered ‘Prophet’. Nevertheless, the question remains about the source of this magic, is it the community or is a divine infinity intervening in the physical world.
In Eberron, mutually conflictive claims can perform miracles.
A DM can decide what the ‘truth’ is, or the DM can intentionally leave the situation mysterious.
Just want to throw that out there since you mentioned Planescape a bit ago. Planescape has this, and the DM can also decide what the "truth" is or leave it myserious.
Athar
("Defiers", "The Lost"), who deny not only the gods' right to pass judgment over mortals, but their very divinity. They claim that the gods (whom they call "powers") are powerful but have limits and do not deserve worship. Instead, Athar priests channel divine power from what they call the "Great Unknown", or what they believe to be the true divine force behind everything. Their headquarters in Sigil is the Shattered Temple, the former temple of the dead god Aoskar. The Athar are broadly derived from real-world atheists, agnostics, and Deists.