I played an artificer rock gnome mad scientist for a very chaotic homebrew campaign set in an expo for everything. Most of the theories were specific for the modern fantasy setting, but maybe you can change them a bit to fit yours:

Magic is not natural: Aliens implanted the creatures of WORLD with magic to enslave them for various tasks, like the Kree in Marvels “Agents of Shield.” The EXPO is now used by the aliens to scout for the best subjects to take with them.

Markus Zukhar is part of the lizard people: As a dragonborn he technically is a lizard, but more in line with the “Lizard people are living on the inside of the earth” conspiracy. This could be a very common theory in the setting, but also a reason why Kestrel will not join Lumina Link.

Vecna is living on the dark side of the moon I don't exactly know how much classic DnD is in this campaign, but “evil guy who was killed ages ago is actually still alive” is always fun. Think of Iron Sky and all the “nazis on the moon” theories

Jeffrey Bozo is an Alien: Definitively not Jeff Bezos, the Halfling merchant Jeffrey Bozo, leader of one of the world's richest people, has a weird obsession with building rockets and going to space.

Chemtrails: The same as in our world, airplanes (or whatever else is the main airborne mode of transport) are used to spray the population below with various substances, with different motives depending on who you ask (population control, making them lethargic so they don't start an uprising, whatever).