Magic of Celestia
Magic is an energy created by the flow of life force processed by living creatures and releases over time. At least when you are not an innately magical being. Magical beings can process and use magic. This also gives them varying degrees of ability to manipulate external sources of magic. Compared to earlier eras magic is much ‘thinner’ in general and far more tame in it’s flow within Celestia and with the thinning of that flow the less any one being can tap at any given time outside their own power.
This is the magic practiced by most beings of Celestia.
High Magic is the kind of reality distorting magic that the Ashuri practiced regularly and many forms of this are known because their Elven slaves learned of how to do such things by watching them. However, outside the gods and similar entities no one is singularly powerful enough to use High Magic without making it into a Ritual.
Other kingdoms learned either by watching the Elves or developing certain concepts on their own. After the Cataclysm only the elves maintained some of their secrets to High Magic. No one else retains the knowledge and changes to the way magic flows means it’s become much harder for these to work. Many a Lich has devoted their undeaths work to recreating High Magic.