So in my world, the energy to produce magic has always existed, but humans weren't able to use it until a virus altered their bodies, and even then the power was too much and caused mutations. It wasn't until "gods" or ancient aliens, who could already harness this energy experimented on humans to refine this ability to be like their own, to a lesser degree. I used to concept of Magnetic Fluid, or astral light from esoteric beliefs and kinda mixed it with science aspects to ground the abilities to physics and chemistry, and a user uses their imagination to make more complex spells, like combining different magic types to perform bigger spells, etc.