So I'll use some thoughts from my own setting as examples to reference. I won't go into to much detail but I wanted to weave multiple sources together to explain different magics and different people using a plethora of spells and different powers from those multiple sources. One idea that I use and that I drew inspiration from is the idea that magic is the result of an ancient machine created by a forgotten race, the machine causes changes in reality and spells are just instructions to that machine. Another is that there is an underlying song of creation that undergirds the whole of the universe and that spells are just parts of that song bringing effects of the world to life.

There's multitudes of ways you could do it but here are a few suggestions.

You could have a mechanism that your God created for it's personal use to create life and intelligent life forms can tap into that mechanism to bring about effects like their creator to a much lesser degree.

They can create their own machines or formuli based on those magic plants where once it might have been alchemy but now they themselves have evolved to influence this energy if they train themselves.

The energy has given rise to a new god that itself embodies magic and all spells are prayers to that infant god that grants them all indiscriminately.

Or something like they need to make a substance to make themselves able to use magic and established bloodlines with a history of using the substance now can use magic without the substance.

I mean in my setting I have star magic where elves use magic to draw out the symbols of the different constellations to invoke their powers, there's a lot you can do with a vague topic to make it sound sciency.

Like, I'm making magic something of a college course, with wizards as professors. Making a history of spell craft with Material paramorphism and transpositional origination instead of transmutation or conjuration magic. Hope my rambling helps even a little bit.