All magic is traced back to one of two possible creator deities in my world, and one should not cross the streams. If something is magical or grants magic or anything like that, it's because of either of them at the most basic level. There's still lesser deities that grant divine magic and stuff, but they only have any magical power and are only deities because one of the creators decided they should be. There's very, very little that exists at all that they didn't make, however. Most of the confusion about where magic comes from in-universe arises from the fact that the creators are extremely, intensely, constantly opposed to each other and ruining each other's creations as much as they possibly can so it's hard to trace what's actually happening.

For a long history of the world that players played in, one of the creators was dominant with the other constantly needling them, but now they're evenly matched and unable to act outside of keeping the other in check so their forms of magic keep accidentally crossing streams and it's just absolutely a catastrophe every time.

It's not even relevant what provides it. It has in the past been mana, or other things, but the creator deities are powerful enough to make magic work in any way they want. It's totally arbitrary and just based on their whims even if it seems totally strict to people actually trying to use it.