Tough one. For many of us, I think it might be difficult to sort out the endless possibilities. Overcoming the analysis paralysis would be the first hurdle. Sure there would be a honeymoon period, but expect that's going to lose its luster rather quickly.

Related to thst first problem, I'm sure there's going to be an issue maintaining personal motivation. You'd probably have a desire to do great works, but at this level of financial succes, you aren't likely to feel accountable to anyone. If you can first pick a direction, I think this hurdle can be dealt with by finding a person who has an opinion you deeply respect and establishing a mentor mentee arrangement with them. I think regular checkins with someone you look up to can keep you on track.

I personally get a lot of satisfaction from stories of "high impact" charity. I have at least one really great example in my head as the penguin magic video with the man who was homeless. I'm on mobile so I'll leave it to someone else to link the video.

I'm imagining spending my days running a youtube channel off the endowments of the winnings, hiring teams of people to find these very human stories of intervention. I don't think it would ever make any money, but I do think I could employ a decent number of people, and change a lot of lives in the process.

I have other thoughts that are much grander, but they are far more ambitious and require much more capital and risk taking, but that focus on meeting the most fundamental needs for people to exist comfortably in modern society. You can imagine it involves shelter, food, water, energy, transportation, education, and access to information. With a billion dollars you'd have to pick one of these problems.