If this is a magical entity, then I would just tell it to give me $100 for every $1,000,000 I use for charitable work that doesn't directly benefit me.
If I give away $1,000,000 100,000 times, that's 100 billion dollars of charitable work. And my net worth would "only" be 10 million dollars, certainly wealthy, but not idiotically wealthy. Plenty for me to invest and have doctor money levels of passive income, but only by giving away the vast vast majority of the money I get.
Or I guess I could just ask the entity to cap my net worth at 10 million dollars, and only give me that money when I have given away some arbitrary amount of money it gives me, like 500 billion dollars or something, Idk.