"The Absolute" is a tool of the Dead Three, created with Netherlise magic from a an elder brain, and is producing their altered mind control tadpoles. When they have spread far enough the dead three will activate the tadpoles and take over the world with an army of mind flayer puppets.
Shar is the main opposition to the Dead Three, the other gods being bound from interfering by Io's Prime Directive. The protagonist is Shar's chosen instrument, she is the one blocking the tadpole's mind control, and who stopped the protagonist falling to their death. This means that all the origin characters (including Custom) are Shar's chosen, not just Shadowheart. The "DM voice" isn't the Absolute, it's Shar.
It's also occurs to me that this being BG3, (possibly former) Sharian cleric Viconia DeVir is likely involved in some way. Rumours of her demise are greatly exaggerated.
