Triple-check that’s it’s real, make sure to secure it in multiple ways, then research charities so I can give most of it away. A couple of million € would already afford me all the luxuries that I could care about.

Not even sure what I’d actually spend money on that would improve my life. I seem to be accumulating medical issues that are difficult to diagnose, let alone treat; not sure that even a billion dollars would actually help much with that (we do have a somewhat sensible healthcare system in my country). I’d probably look into hiring some kind of personal assistant/caretaker/chauffeur, to improve my odds of actually making it to important appointments.