A gift for someone who has everything
The hard part is not generosity. It is finding something they cannot simply order for themselves.
Why the usual answers fail
The person who has everything is not difficult because they are fussy. They are difficult because the ordinary gift categories are all solved for them. They already own the good version of the thing, or they would have bought it the moment they wanted it. Anything you buy in a shop, they could have bought too.
So the gift has to be something that money alone does not settle. Not expensive, but scarce in a way that cannot be manufactured on demand.
Give a fixed point instead of an object
There are 1,440 minutes in a day, and on buy1minute each one belongs to a single person. Not a copy, not an edition of a thousand. One.
That makes a minute a genuinely odd thing to receive. It is not an object to store, insure or dust. It is a fixed point on the day with their name against it, and it comes back around every day for as long as the clock runs.
It also has the quality the difficult recipient usually lacks: once a minute is taken, nobody else can have it. The one they want is available exactly until it is not.
Choosing which minute
The obvious choice is a minute they already carry: the time they were born, the time a child arrived, the minute of a wedding, the minute you met. A time they already know by heart needs no explanation when they see it.
The second choice is a minute that suits them rather than commemorates anything. A round hour, a repeating pattern, a number with a private joke in it. Someone who has everything usually appreciates the wink more than the ceremony.