Yeah a lot of people can use creation magic but it seems to be like a secondary type of magic. When i made her i thought maybe that could be her affinity since Rill paints things. Maybe it can be like craft magic? I don’t know to be honest i’m still playing with this concept but i guess there has to be a component for all her creations and that’d be her affinity? There is also sword magic in universe but again, that’s not an affinity. *sigh* thank you for the list anyway :)
I think in Black Clover universe that creation magic is more a form of magic (as healing magic, reinforcement magic or restraining magic) than a type of magic. When Nozel creates shields or blades he uses creation magic, same for Fuegolelon with his fire column or fire lion.
As you describe it I think your OC’s magic is a bit like Yaomomo’s abilities in MHA or Kaname’s sigil in Darwin’s Game (they both create objects that they know, no matter what they are made of). Right now I don’t think nothing like that exists in the manga. As you said it’s more an “I can control that material and do whatever with it” stuff (for the sword magic it’s more an “I can make a sword with my magic affinity”)
But hey, it’s just a theory, so you can do whatever you like unless Tabata-sensei says “this is true and this is how my universe works!” :)